JPH0698489A - Rotor for servo motor - Google Patents

Abstract

PURPOSE:To achieve that a magnetic resistance in a magnetic gap becomes larger than a magnetic resistance in a part corresponding to a magnetic pole and to reduce a surface magnetic flux density at the outside of a ring magnet by a method wherein the magnetic gap is formed in the outer circumferential face of a core between adjacent magnetic poles in the circumferential direction. CONSTITUTION:In a rotor for servo motor use, a radially anisotropic ring magnet 4 in which a plurality of magnetic poles have been formed in such a way that heteropoles N, S appear alternately is fixed and bonded to the outer circumferential face of a core 1 which is formed of a ferromagnetic material in such a way that its cross-sectional outer circumferential contour is circular. In the rotor for servo motor use, magnetic gaps are formed in the outer circumferential face of the core between adjacent magnetic poles in the circumferential direction. By this constitution, a magnetic resistance in parts of the magnetic gaps between the core 1 in the magnetic poles and the ring magnet 4 becomes larger than a magnetic resistance in positions corresponding to the magnetic poles, and a surface magnetic flux density at the outside of the ring magnet 4 is reduced. Consequently, a change in a magnetic flux density between the magnetic poles is slow, and closely resembles a sine wave. Thereby, a cogging torque can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, robots and NCs.
The present invention relates to a rotor constituting a servo motor used for positioning and speed control of a movable member or a workpiece in a machine tool, etc., and particularly relates to a rotor for a servo motor having a ring magnet of radial anisotropy as a constituent member. Is.

[0002]

2. Description of the Related Art A conventional servomotor rotor generally has a structure as shown in FIG. 4, for example. In FIG. 4, reference numeral 1 denotes a core, which is formed of, for example, a steel material into a cylindrical shape, and shafts 2 are provided at both ends thereof. Reference numeral 3 denotes a permanent magnet whose cross section is formed into an arc segment shape, is magnetized in the thickness direction, and has different poles alternately appearing in the circumferential direction. Fix a plurality. What is shown in FIG. 4 is an example of a four-pole rotor. This rotor is rotatably supported in a plurality of slots on the inner peripheral surface thereof and a stator (not shown) having windings in the slots, and is used as a servo motor.

In the rotor having the above construction, the assembling work for fixing the permanent magnet 3 to the outer peripheral surface of the core 1 is extremely complicated, and the positioning of the permanent magnet 3 also requires a great number of man-hours and time, and the positioning accuracy is further improved. There is also a problem in that high precision cannot be expected in respect of.

In order to solve the above problems, a servomotor rotor having a structure as shown in FIG. 5 has been put into practical use. In FIG. 5, 4 is a ring magnet, for example Nd
-Fe-B system magnet material is used. That is, it is anisotropy in the radial direction through the forming means in the magnetic field.
The core 1 and the ring magnet 4 are fixed to each other with an adhesive.

[0005]

With the structure shown in FIG. 5, it is expected that the assembling work will be extremely easy and the positional accuracy of the magnetic poles can be improved. However, the servo motor rotor having this configuration has the following problems.

First, since the change in magnetic flux density between magnetic poles is steep, uneven rotation or cogging torque increases,
It adversely affects the characteristics of the servo motor. FIG. 6 is a diagram showing the magnetic flux density on the surface of the ring magnet 4. As is clear from FIG. 6, the gradient of the curve between the poles of the magnetic poles N and S is large. As for the servomotor, it is desirable that the curve indicating the magnetic flux density is a sine curve or a curve approximate to a sine curve with some exceptions.

In order to change the magnetic flux density slowly as described above, in the structure shown in FIG. 4, means for forming a small thickness in the vicinity of both end portions of the permanent magnet 3 is adopted. Has been. Alternatively, by forming the radius of curvature of the outer peripheral surface of the permanent magnet 3 to be smaller than the radius of curvature of the inner peripheral surface,
The change of the magnetic flux density between the magnetic poles is made slow to ensure the characteristics of the servo motor. However, FIG.
In the structure as shown in (1), the means for reducing the thickness dimension of the ring magnet 4 between the magnetic poles becomes extremely complicated, and there is a problem that the molding cost or the processing cost rises.

On the other hand, skewing the magnetic poles is also effective as a means for reducing the cogging torque. That is, it is a means for arranging the magnetic poles in the axial direction so as to be inclined with respect to the axis. In the structure shown in FIG. 4, the means for skewing the magnetic poles makes the shape of the permanent magnet 3 complicated, as well as complicates the assembling work and lowers the positional accuracy of the permanent magnet 3. The configuration shown in FIG. 5 can be easily dealt with by devising the orienting means in the molding device and the magnetizing yoke after molding.

However, the skew angle is limited even by the means for skewing the magnetic poles as described above,
There is a problem that the cogging torque cannot be greatly reduced. On the other hand, in recent years, the specifications required for this type of servo motor have become more and more strict, and the emergence of higher performance ones is desired.

In connection with the above, the demand for miniaturization and high performance of the servomotor is gradually increasing, and the ring magnet 4 shown in FIG. 5 made of Nd-Fe-B magnet material is practically used. Has been converted. However, Nd-Fe-B
Since the system magnet material has a negative linear expansion coefficient, there is a problem that the ring magnet 4 is cracked. That is, since the core 1 is usually formed of a steel material having a positive linear expansion coefficient, for example, when the servo motor is in a high temperature atmosphere or after continuous operation for a long time, for example, the rotor is
When the temperature becomes high such as ° C, the core 1 expands while the ring magnet 4 contracts, and a large thermal stress is generated in the ring magnet 4.

It is conceivable to provide a cushioning material between the core 1 and the ring magnet 4 in order to absorb the thermal stress, but the core 1 acts as a back yoke and is a component of the magnetic circuit. Therefore, as a result of the cushioning material being interposed between the core 1 and the ring magnet 4, the magnetic resistance becomes large,
There is a problem in that the surface magnetic flux density of the ring magnet 4 is reduced and the characteristics of the servo motor are degraded.

It is an object of the present invention to solve the problems existing in the above-mentioned prior art, and to provide a rotor for a servo motor which has a small cogging torque and can greatly improve the characteristics.

[0013]

In order to achieve the above object, in the present invention, the outer peripheral surface of a core whose cross-section outer peripheral contour is formed in a substantially circular shape by a ferromagnetic material is provided in a direction parallel to the axis or In a servo motor rotor in which a radially anisotropic ring magnet having a plurality of magnetic poles is fixed so as to extend in an inclined direction and different poles alternately appear in the circumferential direction, the rotors are adjacent to each other in the circumferential direction. A technical means of providing a magnetic gap on the outer peripheral surface of the core between the magnetic poles was adopted.

In the present invention, the magnetic gap can be formed by providing the groove on the outer peripheral surface of the core. Further, in the present invention, the cross-sectional shape of the magnetic gap can be formed in an arc shape, a crescent shape or a convex lens shape. That is, by forming a locally flat surface or a locally cylindrical surface on the outer peripheral surface of the core, the cross-sectional shape as described above can be formed.

In the present invention, the ring magnet is Nd-
It can be formed of an Fe-B based magnet material. Next, the cross-sectional dimension of the magnetic gap in the present invention is selected in accordance with the cross-sectional dimension of the core and the ring magnet that form the rotor, but the height dimension or depth dimension in the diametrical direction is 0.03 mm or more. Preferably. On the other hand, the width in the tangential direction is preferably πd / (2n) or less, where d is the outer diameter of the core or the inner diameter of the ring magnet, and n is the number of magnetic poles. If this value is exceeded, the magnetic flux density that should contribute to the drive torque decreases, which is inconvenient.

[0016]

With the above structure, a magnetic air gap is formed between the core and the ring magnet between the magnetic poles, the magnetic resistance of this portion becomes larger than that at the position corresponding to the magnetic pole, and the surface magnetic flux outside the ring magnet. Density is reduced. Therefore, the change in the magnetic flux density between the magnetic poles becomes slow and the curve approximates to a sine curve, so that the cogging torque can be reduced.

By providing the above-mentioned magnetic gap, thermal stress in the ring magnet due to temperature rise is dispersed, so that cracking of the ring magnet can be prevented.

[0018]

FIG. 1 is an end view of an essential part showing an embodiment of the present invention, in which the same parts are designated by the same reference numerals as in FIG. Figure 1
In the figure, 5 is a groove, and a number corresponding to the number of magnetic poles is provided between the adjacent magnetic poles in the circumferential direction of the ring magnet 4 on the outer peripheral surface of the core 1. The core 1 is formed of SS41, for example, to have an outer diameter of 50 mm, and the groove 5 is formed to have a diametrical depth dimension of 2 mm and 4 mm, respectively, and a tangential width dimension of 12 mm.

The ring magnet 4 is made of an Nd-Fe-B system (HS-30CR manufactured by Hitachi Metals) magnet material and has an outer diameter of 55 mm.
Formed with an inner diameter of 50 mm (however, it can be formed so that it can play with the core 1)
It was fixed to the core 1 via an acrylic adhesive. Since the magnetic poles provided on the ring magnet 4 are magnetized at a skew angle of 30 ° with respect to the axis, the groove 5 provided on the outer peripheral surface of the core 1 is also provided at a skew angle of 30 ° corresponding to the magnetic poles. .

FIG. 2 is a diagram showing the results of measuring the surface magnetic flux density of the ring magnet 4 of the rotor constructed as described above, for example, between the grooves 5 and 5 sandwiching the N pole. Curves a and b in FIG. 2 correspond to those in which the depth dimension of the groove 5 in FIG. 1 in the diameter direction is 2 mm and 4 mm, respectively. The curve c corresponds to the conventional structure shown in FIG.

As is clear from FIG. 2, in the curve c, the magnetic flux density in the vicinity of the gap is large and the gradient is steep. On the other hand, in the curves a and b, the magnetic flux density in the vicinity of the gap is small and the gradient is also reduced, which is similar to a sine curve. This is shown in Figure 1 above.
By providing the groove 5 in the core 1 as shown in FIG.
As a result of the large magnetic resistance between the ring magnet 4 and the ring magnet 4, the outer surface magnetic flux density of the ring magnet 4 in the inter-pole portion decreases.

Since the groove 5 is provided, the cogging torque is 160 g-cm in the conventional case and 110 g-cm and 9 in the cases corresponding to the curves a and b, respectively.
It can be seen that it is reduced to 5 g-cm. In this case, groove 5
The cogging torque is reduced by increasing the depth of the groove 5, but if the depth of the groove 5 is made too large, the magnetic resistance due to the magnetic air gap formed by the groove 5 becomes large, and the magnetic flux density of the entire ring magnet 4 increases. Is reduced, resulting in a decrease in drive torque, which is not preferable.

Next, the function of preventing the ring magnet 4 from cracking by providing the groove 5 in the core 1 shown in FIG. 1 will be described.
With respect to the core 1 and the ring magnet 4 formed as described above in FIG. 1, rotors were assembled by changing the depth dimension of the groove 5 variously, and these were assembled in a thermostatic chamber at 120 ° C. × 4.
A time-keeping rigorous test was performed. A similar severe test was conducted on a conventional rotor having the same specifications and the same dimensions as the rotor shown in FIG.

As a result, in the rotor having the structure shown in FIG. 4, it was confirmed that the ring magnets 4 of all 10 test pieces were cracked. On the other hand, in the rotor having the groove 5 as shown in FIG. 1, no crack of the ring magnet 4 was observed. Although the ring magnet 4 is made of an Nd-Fe-B based magnet material having a negative linear expansion coefficient, the groove 5 is provided, so that the thermal stress generated in the ring magnet 4 is dispersed. Therefore, it can be estimated that the occurrence of cracks can be prevented. The depth of the groove 5 in the diameter direction is
It was confirmed that the ring magnet 4 can be prevented from cracking if it is 0.03 mm or more.

FIG. 3 is an end view of the essential portion showing a modified example of the shape of the magnetic gap formed between the core 1 and the ring magnet 4. First, as shown in FIG. 3 (a), a local flat portion 6 is provided on the outer peripheral surface of the core 1 so that the cross-sectional shape of the magnetic gap is formed into an arc shape. Next, as shown in FIG. 3 (b), a local cylindrical surface 7 having a radius of curvature larger than the radius of curvature of the outer peripheral surface is provided on the outer peripheral surface of the core 1, and the transverse cross-sectional shape of the magnetic gap is formed in a crescent shape. It is a thing. Further, as shown in FIG. 3 (c), a concave local cylindrical surface 8 is provided on the outer peripheral surface of the core 1, and the cross-sectional shape of the magnetic gap is formed into a convex lens shape. In addition, what is shown in FIG. 3D is the groove 5 shown in FIG.
The side surfaces of are parallel surfaces.

In this embodiment, the ring magnet 4 is set to Nd.
Although the example of forming the -Fe-B based magnet material is shown, it may be formed of other rare earth magnet material or ferrite magnet material.

[0027]

EFFECTS OF THE INVENTION Since the present invention has the structure and operation as described above, the following effects can be obtained.

(1) By providing a magnetic gap in the vicinity of the magnetic poles, the magnetic resistance of this portion becomes larger than that at the position corresponding to the magnetic poles, the surface magnetic flux density on the outside of the ring magnet is reduced, and the magnetic flux between the magnetic poles is reduced. As a result of slowing down the change in magnetic flux density, the cogging torque can be greatly reduced.

(2) By providing a magnetic air gap between the core and the ring magnet, the thermal stress generated in the ring magnet can be dispersed, and as a result, cracks generated in the ring magnet can be prevented, and productivity and productivity can be improved. The reliability can be greatly improved.

[Brief description of drawings]

FIG. 1 is an end view of essential parts showing an embodiment of the present invention.

FIG. 2 is a diagram showing a result of measuring a surface magnetic flux density of a ring magnet of a rotor in an example of the present invention.

FIG. 3 is an end view of essential parts showing a modified example of the shape of a magnetic gap formed between a core and a ring magnet.

FIG. 4 is an end view of a main part showing an example of a conventional servo motor rotor.

FIG. 5 is an end view of a main part showing an improved example of a conventional servomotor rotor.

6 is a diagram showing a surface magnetic flux density of a ring magnet of the servo motor rotor shown in FIG.

[Explanation of symbols]

 1 core 4 ring magnet 5 groove

Claims (4)

[Claims] 1. A core, which has a substantially circular cross-section outer peripheral contour formed of a ferromagnetic material, extends on the outer peripheral surface of the core in a direction parallel to the axis or in a direction inclined with different poles alternately appearing in the circumferential direction. In a rotor for a servomotor in which a radial anisotropic ring magnet having a plurality of magnetic poles is fixedly attached, a magnetic air gap is provided on the outer peripheral surface of the core between adjacent magnetic poles in the circumferential direction. Servo motor rotor. 2. The rotor for a servo motor according to claim 1, wherein a magnetic gap is formed by providing a groove on the outer peripheral surface of the core. 3. The servo motor rotor according to claim 1, wherein the magnetic air gap has a cross-sectional shape of an arch, a crescent or a convex lens. 4. The servo motor rotor according to claim 1, wherein the ring magnet is formed of an Nd—Fe—B based magnet material.