ASSEMBLY METHOD AND DEVICE FOR A ROTOR OF AN ELECTRIC MOTOR, AND KITCHEN APPLIANCE

Abstract

A method for positioning magnets on a rotor of an electric motor includes positioning adjacent magnets in a gap-free circle, and then simultaneously radially moving the magnets until a uniform reference gap is created between them. A device includes a plurality of ring segments capable of forming an adjustable annular ring, being simultaneously moveable in radial direction and being capable of moving the magnets from a gap-free circle radially until a uniform reference gap is created between them. A kitchen appliance is also provided.

Claims

1. A method for positioning magnets on a rotor of an electric motor, the method comprising: positioning adjacent magnets in a gap-free circle; and moving the magnets simultaneously radially until uniform reference gaps are created between the magnets.

2. The method according to claim 1, which further comprises pre-positioning the magnets in a circle having circumferential gaps and moving the magnets radially to form the gap-free circle.

3. The method according to claim 1, which further comprises touching the magnets against a circumferential surface of a rotor cage when the uniform reference gaps are achieved.

4. A device for positioning magnets on a rotor of an electric motor, the device comprising: a plurality of ring segments capable of forming an adjustable annular ring; said plurality of ring segments being simultaneously moveable in radial direction; and said plurality of ring segments being capable of moving the magnets radially from a gap-free circle until creating uniform reference gaps between the magnets.

5. The device according to claim 4, wherein said ring segments enable a circumferential movement of each magnet.

6. The device according to claims 4, which further comprises a device for applying a closing force to said plurality of ring segments, said closing force being directed radially in a direction of said gap-fee circle.

7. The device according to claims 6, which further comprises a device for applying an opening force to the magnets, said opening force being directed radially away from said gap-free circle.

8. A kitchen appliance, comprising: an electric motor having a rotor; and adjacent magnets simultaneously radially movable from a gap-free circle until being positioned on said rotor with uniform reference gaps between said magnets.

9. The kitchen appliance according to claim 8, wherein said electric motor is a cook hood motor.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] FIG. 1 is a diagrammatic, perspective view of a rotor of an electric motor according to the prior art;

[0021] FIG. 2 is a perspective view of a rotor according to the invention; and

[0022] FIG. 3 is a plan view illustrating assembly steps of the rotor according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a prior art rotor 1 of an electric motor. The motor is configured as an external rotor motor. The rotor 1 has a cage 2 rotating on a rotation axis 4 around an inner stator (not shown) and carries a plurality of permanent magnets 6 on its inner circumferential surface. The inner stator is equipped with electric coils and is non-rotatable. Spring sheets 8 are positioned in circumferential gaps 10 between the magnets 6 in order to keep the magnets at a distance from each other.

[0024] FIG. 2 shows a preferred embodiment of a rotor 12 of an electric motor. In the following, any direction term such as circumferential refers to a rotation axis 16 of the rotor 12. The motor is configured as an external rotor motor. The rotor 12 has a cage 14 rotating on the rotation axis 16 around an inner stator (not shown) and carries a plurality of segmented magnets 18, in particular arc-shaped permanent magnets, on its inner circumferential surface 20. The non-illustrated inner stator is equipped with electric coils and is non-rotatable. The magnets 18 are held in place on the circumferential surface 20 by glue, for instance. A circumferential gap 22 is shown between two adjacent magnets 18a, 18b. The gaps 22 extents in axial direction and has a uniform extension in circumferential direction (width).

[0025] As is illustrated in FIG. 3, the magnets 18 are positioned on the rotor 12 with the uniform reference gap 22 between them as follows: [0026] In a first step, the magnets 18 are positioned in a radial outer circle (not shown) having random gaps between them. [0027] In a second step, the magnets 18 are moved radially inwards until they are positioned in a gap-free circle (not shown). [0028] In a third step, the magnets 18 are moved simultaneously radially outwards until the uniform reference gap 22 is met between them. In this state, when the uniform reference gap 22 is achieved between all adjacent magnets 18, the magnets 18 are touching a circumferential surface 20 of the rotor cage 14 with their rear surface which facilitates the fixation of the magnets 18 to the inner circumferential surface 20 (see the fourth step). [0029] In a fourth step, the magnets 18 are fixed to the inner circumferential surface 20 of the rotor 12.

[0030] In order to move the magnets adequately, a plurality of triangle-shaped ring segments 24 are provided. As shown, the ring segments 24 form an annular ring that can be maximized or minimized by, preferrable simultaneous, radial movement of them. The magnets 18 can be fixed to the segments 24 or the magnets can be positioned radially outside of the segments 24 but in surface contact with them. The segments 24 are movable in both radial directions 26, 28 by applying a radial closing force 30 to the magnets or by applying a radial opening force 32 to the segments 24 in counter direction. In addition, the magnets 18 are movable in circumferential direction 34 when being in circumferential surface contact with the segments 24 or when fixed on the segments 24.

[0031] In a fifth step, the segments 24 and an inventive device respectively providing the segments 24 are removed after the attachment of the magnets 18 to the rotor 12.

[0032] The closing force 30 and the opening force 32 are applied by respective devices, which are also part of the device according to the invention and are not shown.

[0033] In FIG. 3, the width of the magnets 18 varies. The magnets 18 are shown with different widths only in order to illustrate that the method according to the invention is applicable independently of their extensions in circumferential direction. For the sake of a smooth running, magnets having the same width are preferred.

[0034] Although the method is explained with reference to an external rotor motor, the method of the invention can also be applied to an internal rotor motor by changing the radial movements in counter directions and by positioning the magnets 18 within the ring built by the segments 24. If the rotor 12 is part of an internal rotor motor, an additional fixture can be provided to keep the magnets 18 in position before fixing them to an outer circumferential rotor surface.

[0035] Disclosed are a method for positioning magnets 18 on a rotor of an electric motor, wherein adjacent magnets 18 are positioned in a gap-free circle, and then moved simultaneously radially until a uniform reference gap 22 is met between them, a device having a plurality of ring segments 24 capable of forming an adjustable annular ring which are simultaneously moveable in radial direction and capable of moving the magnets 18 from a gap-free circle radially until a uniform reference gap 22 is met between them, and a kitchen appliance.

[0036] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention.

REFERENCE LIST

[0037] 1 rotor

[0038] 2 cage

[0039] 4 rotation axis

[0040] 6 magnet

[0041] 8 spring sheet

[0042] 10 circumferential gap

[0043] 12 rotor

[0044] 14 cage

[0045] 16 rotation axis

[0046] 18, 18a, 18b magnet

[0047] 20 inner circumferential surface

[0048] 22 gap

[0049] 24 ring segment

[0050] 26 radial direction of the segments

[0051] 28 radial direction of the segments

[0052] 30 closing force

[0053] 32 opening force

[0054] 34 circumferential direction