U.S. patent application number 09/973858 was filed with the patent office on 2002-04-18 for linear type actuator.
This patent application is currently assigned to Minebea Co., Ltd.. Invention is credited to Fujitani, Sakae, Harada, Naoyuki, Matsushita, Kunitake, Suzuki, Yuzuru.
Application Number | 20020043880 09/973858 |
Document ID | / |
Family ID | 18795004 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020043880 |
Kind Code |
A1 |
Suzuki, Yuzuru ; et
al. |
April 18, 2002 |
Linear type actuator
Abstract
In order to reduce cost through reduction in material cost and
improvement of productivity, in a linear type actuator comprising:
a stator unit having coils consisting of wound magnet wires and
housed inside stator sub-assemblies and pole teeth arranged on the
inner circumference thereof; a rotor unit having a field magnet
arranged on the outer circumference thereof and rotatably disposed
so as to oppose the pole teeth with a given gap; an output shaft
attached to a center portion of the rotor unit and movable in the
axial direction thereof; and converting means provided on the
innermost diametral circumferential surface of the rotor unit and
adapted to convert rotary motion of the rotor unit into linear
motion of the output shaft, the converting means is made of a
material different from that of the rotor unit.
Inventors: |
Suzuki, Yuzuru;
(Shizuoka-ken, JP) ; Fujitani, Sakae;
(Shizuoka-ken, JP) ; Harada, Naoyuki;
(Shizuoka-ken, JP) ; Matsushita, Kunitake;
(Shizuoka-ken, JP) |
Correspondence
Address: |
Jay F. Moldovanyi, Esq.
Fay, Sharpe, Fagan, Minnich & McKee, LLP
7th Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Assignee: |
Minebea Co., Ltd.
|
Family ID: |
18795004 |
Appl. No.: |
09/973858 |
Filed: |
October 10, 2001 |
Current U.S.
Class: |
310/12.14 ;
310/80 |
Current CPC
Class: |
Y10T 29/49012 20150115;
Y10T 74/18664 20150115; H02K 7/06 20130101; Y10T 74/18576
20150115 |
Class at
Publication: |
310/12 ;
310/80 |
International
Class: |
H02K 041/00; H02K
007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2000 |
JP |
315993/2000 |
Claims
What is claimed is:
1. A linear type actuator comprising: a stator unit having coils
consisting of wound magnet wires and housed inside stator
sub-assemblies and pole teeth arranged on an inner circumference
thereof; a rotor unit having a field magnet arranged on an outer
circumference thereof and rotatably disposed so as to oppose said
pole teeth with a given gap; an output shaft attached to a center
portion of said rotor unit and movable in the axial direction
thereof; and converting means provided on an innermost diametral
circumferential surface of said rotor unit and adapted to convert
rotary motion of said rotor unit into linear motion of said output
shaft, wherein said converting means is made of a material
different from that of said rotor unit.
2. The linear type actuator as set forth in claim 1, wherein said
converting means is configured with a plurality of straight sides
and has corners thereof rounded.
3. The linear type actuator as set forth in claim 1, wherein said
rotor unit is integrally constituted by insert molding said field
magnet, magnet stoppers adapted to hold said field magnet and also
to protect end corners thereof, and said conversion means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a linear type actuator, in
which an output shaft is adapted to move linearly, and more
particularly to a linear type actuator which can be manufactured
with reduced cost through reduction in material cost and
improvement in productivity.
[0003] 2. Description of the Prior Art
[0004] In recent years, a direct drive is required for high
performance in various apparatuses, and a linear type actuator has
been employed for linear control.
[0005] FIG. 1A shows a longitudinal section of a conventional
linear type actuator using a PM (permanent Magnet) stepping motor
and FIG. 1B shows an enlarged view of a circled portion B of the
linear type actuator shown in FIG. 1A.
[0006] Referring to FIGS. 1A and 1B, a rotor unit 50 is rotatably
arranged inside a stator unit 40, a field magnet 51 is insert
molded in the rotor unit 50, and a female screw 52 is formed on the
innermost diametral circumferential surface of an insert molded
resin portion 56. A male screw 62 is formed on an output shaft 60,
and engages with the female screw 52. Due to an antirotation pin 31
preventing the output shaft 60 from rotating, the output shaft 60
is moved in an axial direction by the rotation of the rotor unit
50.
[0007] However, the conventional linear type actuator as
abovementioned has the following problems:
[0008] Since the female screw 52 is required to feature small
coefficient of friction, high wear resistance and excellent
dimensional stability, insert molding thereof requires a
high-quality and therefore expensive resin material pushing up the
cost. Furthermore, since its molding conditions include high
temperature and high pressure, the workability of insert molding
the female screw 52 together with the field magnet 51 is
deteriorated and the insert molded product must be rotated to be
removed for the purpose of forming the female screw 52. This
inevitably complicates a mold and causes an increase in the number
of man-hours, which makes it difficult to streamline parts and
stabilize the quality of parts as well at the same time.
[0009] Further problem is that since the female screw 52 is formed
at the time of producing the rotor unit 50, the productivity of the
insert molding is poor, thereby increasing the number of
man-hours.
SUMMARY OF THE INVENTION
[0010] The present invention was made considering the above
problems, and it is an object of the present invention to provide a
linear type actuator in which a rotor unit is manufactured by
insert molding a nut serving as a motion converting means which
plays an important part in linear type actuator, a field magnet and
a magnet stopper, so as to reduce the material cost and improve the
productivity, thereby achieving a cost reduction.
[0011] According to the present invention, in a linear typeactuator
comprising: a stator unit having coils consisting of wound magnet
wires and housed inside stator sub-assemblies and pole teeth
arranged on the inner circumference thereof; a rotor unit having a
field magnet arranged on the outer circumference thereof and
rotatably disposed so as to oppose the pole teeth with a given gap
therebetween; an output shaft attached to a center portion of the
rotor unit and movable in the axial direction thereof; and a nut as
a motion converting means (hereinafter referred to as converting
means) provided on the innermost diametral cicumferential surface
of the rotor unit and adapted to convert rotary motion of the rotor
unit into linear motion of the output shaft, the converting means
is made of a material different from that of the rotor unit.
[0012] The converting means is configured with a plurality of
straight sides and has rounded corners thereof formed at joints of
the sides.
[0013] The rotor unit is integrally constituted by insert molding
the field magnet, magnet stoppers adapted to hold the field magnet
and also to protect end corners thereof, and the converting
means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A shows a longitudinal sectional view of a
conventional linear type actuator using a PM stepping motor;
[0015] FIG. 1B shows an enlarged view of a circled portion B of the
linear type actuator shown in FIG. 1A;
[0016] FIG. 2A shows a top plan view of the entire structure of a
linear type actuator using a PM stepping motor according to the
present invention;
[0017] FIG. 2B shows a longitudinal sectional view of the linear
type actuator shown in FIG. 2A;
[0018] FIGS. 2C and 2D show enlarged views of circled portions C
and D of the linear type actuator shown in FIG. 2B,
respectively;
[0019] FIG. 3 shows an example of a converting means used in the
linear type actuator according to the present invention;
[0020] FIGS. 4A, 4B and 4C show other examples of the converting
means proposed in the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The present invention will now be described by reference to
the accompanying drawings.
[0022] FIG. 2A shows a top plan view of the entire structure of a
linear type actuator using a PM stepping motor according to the
present invention, and FIG. 2B shows a longitudinal sectional view
of the linear type actuator shown FIG. 2A taken along line A-A.
[0023] A stator unit 10 comprises two stator sub-assemblies 12
attached to each other in a back to back manner to form two layer
construction and integrally molded with a resin material. Each
stator sub-assembly 12 is constructed by two kinds of stator yokes
formed of a soft magnetic steel sheet worked by sheet metal
processing so as to have pole teeth 11 on the inner circumference
and to house a coil 14. In this integral molding process, a rear
plate 13 which constitutes one end face of the stator unit 10 and
has a bearing in its central portion is formed by a resin material
for integration at the same time. Thus, a high coaxial precision
with respect to the pole teeth formed on the inner circumference of
the stator unit 10 can be secured, thereby reducing the number of
processes and parts and at the same time enhancing the
precision.
[0024] The coils 14 housed inside the stator unit 10 each comprise
a bobbin 16 made of a resin material such as PBT (Polybutylene
telephthalate) resin and a magnet wire wound thereon, and a cover
ring 15 which is dimensioned sufficient to cover the height of the
coil 14 is arranged outside the coil 14. The coils 14 are connected
to a connector 17 via an intermediary substrate 34, and a pulse
drive voltage is applied to the coil 14 through the connector
17.
[0025] A rotor unit 20 as a rotating body has a magnet stopper 22
made of a metal plate, arranged on both end faces of the field
magnet 21 for preventing the field magnet 21 from dropping and
adapted to increase the holding force between the field magnet 21
and the rotor unit 20 and to stabilize the size thereof, and a nut
23 as a converting means arranged in the center thereof and adapted
to convert rotary motion into linear motion. The magnet stopper 22
and the nut 23 are insert molded to integrally constitute the rotor
unit 20. For the nut 23, a resin material such as PPS
(Polyphenylene sulfide) resin containing fluorine having small
friction coefficient and high wear resistance is used. Reference
numeral 26 designates an insert molded resin portion such as PBT
resin, and bearings 24, 25 are provided on both end faces thereof
to rotatably hold the rotor unit 20.
[0026] As clearly shown in FIG. 2C, an output shaft 30 with a male
screw 62 is arranged in the center of the rotor unit 20 such that
the male screw 62 engages with the nut 23. The output shaft 30 has
antirotation pin 31 in the midway thereof and a shaft head 32
provided on a tip end thereof.
[0027] A front plate 18 having a pawl 18a on the outer periphery
thereof is attached to an end face of the stator unit 1 located on
the output shaft side by projection welding.
[0028] The rotor unit 20 and the output shaft 30 will be assembled
into the stator unit 10 in the following manner. The rotor unit 20
and the output shaft 30 are put into the stator unit 10, then a
housing 33 is attached and caulked with the pawl 18a to be fixed.
Then the shaft head 32 is attached to the tip end of the output
shaft 30, and lubricant is appropriately applied to each sliding
portion to prevent decrease in efficiency and at the same time to
ensure durability.
[0029] Operation of the linear type actuator of the present
embodiment is described.
[0030] When a pulse drive voltage is applied to the coil 14 through
the connector 17, the rotor unit 20 rotates by interaction of the
magnetic flux of the coil 14 and the field magnet 21. Although the
nut 23 also rotates due to the rotation of the rotor unit 20, the
output shaft 30 is prevented from rotating by the antirotation pin
31, so that the output shaft 30 moves only in an axial
direction.
[0031] FIG. 3 shows an example of the nut 23 as a converting means
used in the present invention.
[0032] The nut 23 shown here is a kind of hexagon nut in which
roundness is given at each corner so that concentration of stress
exerted on the insert molding resin can be avoided. By use of the
nut 23 made of an expensive resin material of high quality such as
PPS resin containing fluorine, it is possible to use less amount of
such resin material of high quality for the major portion of the
rotor unit 20.
[0033] FIG. 4A shows another example 23a of converting means of a
quadrangular shape, FIG. 4B shows still another example 23b of
converting means of a spline-shape and FIG. 4C shows a further
example 23c of converting means of a cylindrical shape having plane
cross sections. In these examples, roundness is given at each
corner. It is to be noted that these shapes of the converting means
are merely examples and are not limitative.
[0034] As described above, in the linear type actuator of the
present invention, a nut or converting means is made of a resin
material having small coefficient of friction, high wear resistance
and excellent dimensional stability, and is provided with a shape,
for example, hexagon which is effective for prevention of rotation.
The nut is insert molded together with a field magnet using an
inexpensive resin material to constitute a rotor unit. In this
insert molding process, a female screw is not formed, so its die
structure is simple and processing time is short.
[0035] Therefore, in the linear type actuator of the present
invention, cost can be reduced through reduction in material cost
and improvement of productivity.
[0036] Since a material of the insert molding resin of the
conventional rotor unit 50 is different from a resin material of a
stator unit 10, both resin materials are different in expansion
coefficient from each other thereby limiting the working
temperature range. With the linear type actuator of the present
invention, resin materials having the same characteristic can be
employed, so that the quality of the resin materials can be
stabilized.
[0037] In the embodiment described above, the nut 23 has been
molded by a resin material whose coefficient of friction is small
and whose wear resistance is high, but any kind of nuts on the
market can be employed.
[0038] According to the present invention, in a linear type
actuator comprising: a stator unit having coils consisting of wound
magnet wires and housed inside stator sub-assemblies and pole teeth
arranged on the inner circumference thereof; a rotor unit having a
field magnet arranged on the outer circumference thereof and
rotatably disposed so as to oppose the pole teeth with a given gap
therebetween; an output shaft attached to a center portion of the
rotor unit and movable in the axial direction thereof; and
converting means provided on the innermost diametral
circumferential surface of the rotor unit and adapted to convert
rotary motion of the rotor unit into linear motion of the output
shaft, the converting means is made of a material different from
that of the rotor unit. Thus, the cost can be reduced through a
reduction in the material cost and an improvement of the
productivity.
[0039] The nut used in the present invention is configured with a
plurality of straightsides and has corners thereof rounded, whereby
stress concentration due to contraction of the molded material is
hard to occur. Therefore the nut has an antirotation function, so
that appropriate insert molding can be realized.
[0040] Since the rotor unit is integrally constituted by insert
molding the field magnet, magnet stoppers adapted to hold the field
magnet and also to protect end corners thereof, and the nut, the
rotor unit can be manufactured ensuring stable quality.
* * * * *