JP2001214858A - Driving device having linear motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving device having a linear motor capable of checking exertion of a magnetic field other than a prescribed magnetic field on a magnetic detecting part and accurately detecting a position of a driving object. SOLUTION: This driving device includes the linear motor 2 for reciprocatively driving the driving object, a rod part 7 integrally installed on the driving object and transmitting driving force from the linear motor 2, a magnet part 9 and the magnetic detecting part 10 for detecting the magnetic field of the magnet part 9, and is provided with a position detecting means 13 for detecting the position of the driving object and a magnetic shielding part 11 for surrounding the position detecting means 13 and checking exertion of the magnetic field of the linear motor 2 on the magnetic detecting part 10. The magnetic shielding part 11 is composed of a bottomed cylindrical body having respectively through holes for penetrating the rod part 7 in both end parts. The magnet part 9 is integrally installed in the rod part 7 surrounded by the magnetic shielding part 11. The magnetic detecting part 10 is arranged so as to be opposed to the magnet part 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device having a linear motor, and more particularly, to a linear motor using a magnetic shield structure for preventing a magnetic field other than a predetermined magnetic field from reaching a magnetic detecting portion of a magnetic sensor. The present invention relates to a drive device provided with a linear motor for preventing a magnetic field from reaching a magnetic detection section of a magnetic sensor.

[0002]

2. Description of the Related Art In recent years, for example, in a cooling device such as a refrigerator, as a device for compressing expanded refrigerant gas,
A linear compressor that performs gas compression by reciprocating a piston in a cylinder by a linear motor has been developed.

An example of a conventional linear compressor will be described with reference to the drawings. As shown in FIG. 5, in the conventional linear compressor, a cylindrical casing 110
Cylinders 111a, 111a at the upper end and the lower end, respectively.
11b is provided. The cylinders 111a, 11
The pistons 112a and 112b are respectively inserted into 1b.

A compression chamber 1 is provided between the heads of the pistons 112a and 112b and the upper walls of the cylinders 111a and 111b.
13a and 113b are formed.

The cylinders 111a and 111b have:
Suction valves 114a, 114b and discharge valves 115a, which open and close according to the gas pressure in the compression chambers 113a, 113b,
115b is attached.

The pair of pistons 112a and 112b
One end and the other end of the rod 116 are connected to each other. The rod 116 has a pair of bearings 11.
7a, 117b and coil springs 118a, 118b, the casing 110 and the cylinders 111a, 1
11b is reciprocally supported.

[0007] The linear compressor is provided with a linear motor 120 for reciprocatingly driving the pistons 112a and 112b. The linear motor 120 is a voice coil motor, and includes a fixed portion including a yoke portion 110a and a permanent magnet 121, and a movable portion including a coil 123 and a cylindrical support member. The yoke part 110a forms a part of the casing 110.
The permanent magnet 121 is fixed to the inner peripheral wall of the yoke 110a.

One end of the support member 124 is connected to the outer peripheral wall of the permanent magnet 121 and the yoke portion 110a and the yoke portion 11a.
0a is loosely inserted into the cylindrical space between the inner peripheral wall and the other end of the rod 116a. Coil 1
23 is attached to one end of the support member 124 and faces the permanent magnet 121.

As shown in FIG. 6, a magnet plate 142 in which N poles and S poles are alternately magnetized at a constant pitch is fixed to an arm 260 projecting from the center of the rod 116. On the other hand, the convex portion 2 formed on the inner surface of the casing 110
00, the MR element 1
41 are attached. The displacement sensor 14 is constituted by the MR element 141 and the magnet plate 142.

In the above-described linear compressor, the masses of the pistons 112a and 112b, the rod 116, the coil 123 and the support member 124, the compression chambers 113a and 113b
Has a resonance frequency determined by the spring constant of the gas, the spring constant of the coil spring 118, and the like. This resonance frequency is usually set near the frequency of commercial power (for example, 60 Hz). By driving the linear motor 120 at this resonance frequency, the gas can be compressed alternately in the pair of compression chambers 113a and 113b. A conventional linear compressor is configured as described above.

[0011]

The MR element 141 of the displacement sensor 14 is provided with a magnetic shielding plate 150 made of iron or the like to prevent the magnetic field of the linear motor 120 from reaching the MR element 141. It is provided on the back surface of the MR element 141 that is not opposed to 142.

On the other hand, the magnetic field of the linear motor 120 includes a DC magnetic field generated by the permanent magnet 121 and an AC magnetic field generated by the coil 123, and both have a magnetic field strength of 10 G or more.

However, the conventional configuration in which a magnetic shielding plate is provided on the back surface of the MR element 141 is not enough to shield such a magnetic field. Further, when a plurality of types of magnetic shielding plates having different shielding strengths are directly laminated, it is not enough to shield a DC magnetic field having the above-mentioned magnetic field intensity, and further, it is impossible to shield an AC magnetic field.

Therefore, the magnetic field of the linear motor 120 is M
As far as the R element 141, the MR element 141 could not correctly detect the magnetic field of the magnet plate 142, and could not correctly grasp the positions of the pistons 112a and 112b in the linear compressor. As a result, the maximum stroke of the piston could not be controlled well, and the capacity of the linear compressor could not be maximized.

Further, when the displacement sensor 14 is located on the radially inner side of the linear motor 120 in order to reduce the axial dimension of the linear compressor, the influence of the DC magnetic field and the AC magnetic field appears particularly. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to prevent a magnetic field other than a predetermined magnetic field from reaching a magnetic detecting section and to accurately detect the position of a driven object. The object of the present invention is to provide a drive device provided with:

[0017]

A driving apparatus having a linear motor according to the present invention is provided with a linear motor for reciprocatingly driving a driven object, and a linear motor attached to the driven object, A rod section for transmitting a driving force, a magnet section, and a magnetic detection section for detecting a magnetic field of the magnet section; a position detection section for detecting the position of the driven object; A magnetic shielding unit for preventing a magnetic field of a motor from reaching the magnetic detection unit;
The magnetic shielding portion is formed of a bottomed cylindrical body having through holes through which the rod portion penetrates at both ends thereof,
The magnet section is integrally attached to the rod section surrounded by the magnetic shielding section, and the magnetic detection section is arranged so as to face the magnet section.

By using this configuration, the magnet portion of the position detecting means and the magnetism detecting portion are housed in the space inside the magnetic shielding portion made of a bottomed cylindrical body. It is possible to prevent the magnetic field from being applied to the magnetic detection unit itself by being shielded by the state body. Also,
The magnetic field is prevented from reaching the magnet section, and the magnetic field of the magnet section can be prevented from being affected. Therefore,
The magnetic field of the magnet unit can be detected without being affected by other magnetic fields, and the detection accuracy is improved.

More specifically, the position detecting means may be located on the radially inner side of the linear motor. Thereby, the axial dimension of the driving device can be reduced.

The magnetic shielding portion is made of a magnetic material, and has a first shielding member for shielding a magnetic field having a magnetic field intensity in a first range, and a first shielding member provided outside the first shielding member so as to cover the first shielding member. A second field that is stronger than the magnetic field strength of the first range.
A second shielding member made of a magnetic material that shields a magnetic field intensity in a range, and a third shielding member made of a nonmagnetic material and provided between the first shielding member and the second shielding member. It is good. And the first shielding member includes:
It is preferable that permalloy is a main component, and the second shielding member is a main component of iron.

By using this configuration, since the first shielding member and the second shielding member are not directly laminated,
A magnetic field of 0 G or more is first weakened by the second shielding member,
The magnetic field of about several G is further weakened by the second shielding member, and the invading magnetic field can be effectively weakened.

Further, the magnetic shielding portion is made of a magnetic material, is provided inside the first shielding member, and is made of a magnetic material that shields a third range of magnetic field strength lower than the first range of magnetic field strength. A fourth shielding member and a non-magnetic material,
A fifth shielding member provided between the first shielding member and the fourth shielding member.
Preferably, the first and fourth shielding members are mainly composed of permalloy, and the second shielding member is mainly composed of iron.

By using this configuration, the magnetic field weakened by the first shielding member and the second shielding member is further reduced, and the invading magnetic field can be reduced more effectively.

Preferably, the third and fifth shielding members are made of a conductive material. According to this configuration, an eddy current due to the AC magnetic field is generated in the third and fifth shielding members, and the AC magnetic field can be effectively blocked.

Further, in the linear motor, a movable body integrally fixed to the rod portion and having a permanent magnet on its outer periphery is disposed in a gap formed in a part of a magnetic circuit including an electromagnetic coil and a magnetic frame. Alternatively, a configuration may be employed in which the driven object is reciprocated by supplying an alternating current of a predetermined frequency to the electromagnetic coil. According to this configuration, the AC magnetic field can be effectively cut off reliably without fail even in a magnet movable linear motor in which the influence of the AC magnetic field on the position detecting means arranged on the radially inner side of the linear motor is large. .

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a driving device having a linear motor according to an embodiment of the present invention;
An example in which the invention is applied to a linear compressor will be described. FIG. 1 shows a linear motor 2 in a linear compressor,
2 shows a cross-sectional structure of a main part including a magnet (magnet part) 9 and a sensor element (magnetic detection part) 10. As shown in FIG. 1, a linear motor 2 in a linear compressor 1 is a magnet movable type motor,
It has a fixed portion including the yoke portion 6a and the coil 5, and a movable portion including the permanent magnet 4 and the cylindrical support member 3.

The yoke 6a forms a part of the casing 6. The coil 5 is fixed to the inner peripheral wall of the yoke 6a. One end of the support member 3 is loosely inserted into a cylindrical space between the coil 5 and the outer inner peripheral wall of the yoke 6a, and the other end is connected to the rod 7. The permanent magnet 4 is attached to one end of the support member 3 and faces the coil 5. The rod 7 is reciprocated in the axial direction by the linear motor 2.

On the radially inner side of the linear motor 2, there is disposed a magnetic shielding portion 11 made of a bottomed cylindrical body having a through hole through which the rod 7 penetrates at both ends. Position detecting means 13 for detecting the position of a piston (not shown) fixed to one side of the direction in which the rod 7 reciprocates is disposed inside the magnetic shielding portion 11.

The position detecting means 13 includes a magnet 9 integrally attached to the outer peripheral surface of the rod 7 and a sensor element 10 attached to the inner peripheral wall of the magnetic shielding portion 11 and arranged to face the magnet 9. It is composed of

Next, the structure of the magnetic shield 11 will be described in detail. As shown in FIG.
It has a layer structure. A fourth shielding member 14d made of permalloy C (composition ratio: 78% by weight of nickel, 22% by weight of iron) is provided inside, and a conductive material made of a nonmagnetic material, for example, aluminum or the like is provided outside the fourth shielding member 14d. A fifth shielding member 14e made of a conductive material is provided. A first shielding member 14a made of permalloy B (composition ratio: nickel 45% by weight, iron 55% by weight) having a different composition ratio from the fourth shielding member 14d is provided outside the fifth shielding member 14e. The third shielding member 14 made of the same material as the fifth shielding member 14e is provided outside the first shielding member 14a.
c is provided. And the third shielding member 14c
Is provided with a second shielding member 14b made of iron. And the magnetic shielding part 11 is provided with the bottom part 11a in which the through-hole 13 which the rod 7 penetrated was opened, and the lid part 11b.

As shown in FIG. 3, iron used as the second shielding member 14b has a DC magnetic field strength of G to 100G.
The first shielding member 1 is suitable for shielding a magnetic field of
The permalloy B used as 4a is suitable for shielding a magnetic field of about several mG to several G, and the fourth shielding member 14d
Is suitable for shielding a magnetic field of about several μG to about 1 G. Therefore, by disposing the shielding member made of iron outside the shielding member made of Permalloy B or C, a relatively strong magnetic field is first weakened by the shielding member made of iron, and the shielding member made of Permalloy B or Permalloy C is further provided. Weakened by Thereby, a DC magnetic field of 10 G or more can be reduced to several mG or less. Here, FIG. 3 is an explanatory diagram showing an optimum use range of each shielding member for a DC magnetic field.

On the other hand, the third shielding member 14c and the fifth shielding member 1 made of a conductive non-magnetic material such as aluminum.
In 4e, an eddy current is generated by the AC magnetic field. Accordingly, the AC magnetic field can be weakened, and the AC magnetic field of 10 G or more can be weakened to several mG or less together with the shielding effect of the first shielding member 14a, the second shielding member 14b, and the fourth shielding member 14d.

As shown in FIG. 4, the DC magnetic field 12a and the AC magnetic field 12b generated by the linear motor 2 are weakened by the magnetic shield 11 or the magnetic shield 11
The lines of magnetic force are guided along the shielding member made of the magnetic material (see the arrow in the figure). Therefore, the magnetic shielding unit 1
1, the magnetic field in the space becomes several mG or less, and the linear motor 2
Can be prevented from reaching the sensor element 10. As a result, the sensor element 10 can detect the magnetic field of the magnet 9 without being affected by the external magnetic field, and can accurately grasp the position of the piston (not shown).

By accurately grasping the position of the piston, the maximum stroke of the piston can be controlled, and the performance of the linear compressor can be maximized.

Since the magnetic shield 11 is formed of a cylindrical body having a bottom as described above, the magnetic fields 12 a and 12 b generated by the linear motor 2
The 4a and the lid portion 14b prevent the rod 7 from entering the inside of the bottomed cylindrical body from the axial direction, and the lines of magnetic force are guided along the magnetic shielding portion 11.

In the above embodiment, aluminum was used as an example of the conductive non-magnetic material.
For example, even when a material having a high electric conductivity such as copper is applied, the AC magnetic field can be effectively shielded. Further, such a conductive non-magnetic material may be provided inside the fourth shielding member 14d made of Permalloy C, or may be further provided outside the second shielding member 14b made of iron. In this case, The AC magnetic field can be more effectively shielded.

In the above embodiment, the magnetic shield 1
Although the magnetic shield unit 1 has a five-layer structure as an example, the magnetic shield unit is not limited to this, and has a three-layer structure using the first shield member 14a, the second shield member 14b, and the third shield member 14c. Even when 11 is used, the same effect can be expected. However, the magnetic field shielding effect is slightly reduced as compared with the five-layer structure. Further, only the bottom part 14a and the lid part 14b of the magnetic shielding part 11 may have a single-layer structure of the second shielding member 14b. In this case, manufacture and assemblability are improved. Further, even when the magnetic shielding portion 11 is not the five-layer structure or the three-layer structure but has a single-layer structure of the second shielding member 14b, a magnetic shielding plate is provided on the back surface of the magnetic detection portion as in the related art. Compared with the configuration, the magnetic field of the magnet unit can be detected without being affected by other magnetic fields.

In addition, in the above-described embodiment, the case where the magnetism of the linear motor of the linear compressor is shielded has been described as an example. However, the present invention is not limited to the linear compressor, but is widely applied to a drive device having a linear motor. Is possible.

The description of the above embodiment disclosed this time is as follows.
It is for the purpose of illustrating the invention and should not be construed as limiting the invention set forth in the claims or reducing the scope thereof. In addition, the configuration of each part of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[0040]

As described above, according to the present invention, the magnetic field of the linear motor is shielded by the magnetic shielding portion formed of a bottomed cylindrical body, and the magnetic field is prevented from reaching the magnetic detection portion itself of the position detecting means. can do. Therefore, the magnetic field of the magnet unit can be detected without being affected by other magnetic fields, and the detection accuracy is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a linear compressor according to an embodiment of the present invention.

FIG. 2 is a perspective view of a magnetic shield of the linear compressor shown in FIG.

FIG. 3 is a diagram showing an optimum range of DC magnetic field shielding by iron or permalloy.

FIG. 4 is a schematic diagram showing a magnetic field of a linear motor of a linear compressor.

FIG. 5 is a cross-sectional view of a conventional linear compressor.

FIG. 6 is a partially enlarged view of the linear compressor shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Linear compressor 2 Linear motor 3 Support member 4 Coil 5 Permanent magnet 6a Yoke part 6 Casing 7 Rod (rod part) 9 Magnet (magnet part) 10 Sensor element (magnetic detection part) 11 Magnetic shielding part 11a Bottom part 11b Cover part 12a DC magnetic field 12b AC magnetic field 13 Position detecting means 14a Permalloy B (first shielding member) 14b Iron (second shielding member) 14c Nonmagnetic material (third shielding member) 14d Permalloy C (fourth shielding member) 14e Nonmagnetic material ( Fifth shielding member)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference)

Claims (9)

[Claims] 1. A linear motor for reciprocatingly driving a driven object, a rod unit integrally attached to the driven object and transmitting a driving force from the linear motor, a magnet unit, and a magnet unit. A magnetic detection unit for detecting a magnetic field,
Position detecting means for detecting the position of the driven object, and a magnetic shielding section surrounding the position detecting means and preventing the magnetic field of the linear motor from reaching the magnetic detecting section, The magnet part is integrally attached to the rod part surrounded by the magnetic shielding part, and the magnet part is provided with a bottomed cylindrical body having through holes through which the rod part penetrates at both ends thereof. A drive unit provided with a linear motor, wherein the unit is disposed so as to face the magnet unit. 2. The drive device according to claim 1, wherein the position detection unit is located on a radially inner side of the linear motor. 3. The magnetic shielding part is made of a magnetic material,
A first shielding member for shielding a magnetic field having a first range of magnetic field strength;
A second shielding member that is provided outside the first shielding member so as to cover the first shielding member and is made of a magnetic material that shields a magnetic field intensity in a second range stronger than the magnetic field intensity in the first range; The first shielding member and the second shielding member are made of a magnetic material.
The drive device provided with the linear motor according to claim 1 or 2, further comprising a third shielding member provided between the linear motor and the shielding member. 4. The driving device according to claim 3, wherein the first shielding member is mainly composed of permalloy, and the second shielding member is mainly composed of iron. 5. The driving device according to claim 3, wherein the third shielding member is made of a conductive material. 6. The magnetic shielding part is made of a magnetic material,
A fourth shielding member, which is provided inside the first shielding member and is made of a magnetic material for shielding a third range of magnetic field intensity weaker than the first range of magnetic field intensity, and a nonmagnetic material; 5. A fifth shielding member provided between the member and the fourth shielding member, respectively.
A driving device comprising the linear motor according to any one of the preceding claims. 7. The linear motor according to claim 6, wherein the first shielding member and the fourth shielding member are mainly composed of permalloy, and the second shielding member is mainly composed of iron. Drive. 8. The device according to claim 6, wherein the third and fifth shielding members are made of a conductive material.
A driving device provided with the linear motor according to 1. 9. The linear motor, wherein a movable body fixed integrally to the rod portion and having a permanent magnet on its outer periphery is disposed in a gap formed in a part of a magnetic circuit including an electromagnetic coil and a magnetic frame. 9. A driving device comprising a linear motor according to claim 1, wherein the driven object is reciprocated by supplying an alternating current having a predetermined frequency to the electromagnetic coil.