Rotating electric machine

Abstract

Rotating electrical machine. Rotating electrical machine comprising a rotor (1) and a stator (2), the stator (2) having slots (21) in which electrical conductors are housed, the slots (21) being open towards an air gap (23) formed between the rotor and the stator, the machine comprising a magnetic ring (3) located in the air gap (23) in contact with an internal surface of the stator, the magnetic ring (3) having a permeability configured to prevent the passage of a magnetic flux under normal operating conditions of the machine, particularly in a circumferential direction of the magnetic ring (3). Figure for the abbreviation: Figure 1

Description

Title of the invention: Rotating electric machine technical field

[0001] The present invention relates to rotating electrical machines, in particular permanent magnet synchronous machines.

[0002] In a rotating electrical machine with permanent magnets, for example a motor, a cogging torque effect can occur. This phenomenon is due to the interaction between the slots in the machine's stator mass and the rotor's permanent magnets. The openings of the slots towards the air gap between the stator and the rotor can cause variations in the magnetic permeability of the air gap, resulting in different magnetic resistances depending on the rotor's position relative to the stator. The magnetic flux of the rotor's permanent magnets constantly seeks the shortest closed path. Consequently, some rotor positions are magnetically more stable than others. This periodic variation in magnetic stability manifests itself as the cogging torque effect.This phenomenon, although inherent to many permanent magnet motors, is undesirable as it can lead to uneven motor operation, vibration, and noise. This can be disruptive in applications requiring high stability or precision, such as surgical robots. Previous technique

[0003] Techniques such as angular offset at the rotor ("skewing"), the selection of a specific combination of slots and poles, or the combination of multi-shaped permanent magnets can be used to minimize the effects of toothing. However, angular offset at the stator risks increasing the winding resistance. Angular offset at the rotor is relatively simple to implement, especially when a ring magnet is used. However, motor performance can be reduced as the tilt angle increases. Combining hybrid magnet shapes to reduce the toothing effect has the drawback of significantly increasing the machine manufacturing cost because more permanent magnet references must be kept in place and managed.

[0004] Magnetic shims can also be placed in the slot openings to smooth out the air gap reluctance. However, this method can only be used in large motors with slots that have a large opening to the air gap, allowing for the positioning of the shims. In a motor of With its small inner diameter, it is difficult to properly position the magnetic wedge in the engine.

[0005] It may also be considered to use closed-contour slots on the air gap side between the rotor and the stator. This technique allows for a weak ratcheting effect. However, since the winding must then be carried out from outside the stator teeth, the electrical conductor filling rate may be reduced. In this case, the rated torque of the machine may also be reduced. Also, the winding process may be more complicated. The winding must be pre-formed and inserted into the slots, and then the slots must be closed on the side opposite the air gap by a yoke.

[0006] There is therefore a need for a rotating electrical machine with a simple structure and low cost, while also reducing the effect of notching. Summary of the invention

[0007] The invention aims to meet this need, and it achieves this, according to a first aspect, by means of a rotating electrical machine comprising a stator and a rotor.

[0008] The stator has slots in which electrical conductors are housed. The slots open towards an air gap formed between the rotor and the stator. The machine includes a magnetic ring located in the air gap, notably in contact with an internal surface of the stator. The magnetic ring may have a permeability configured to prevent the passage of magnetic flux under normal operating conditions of the machine, particularly in a circumferential direction around the ring.

[0009] According to the invention, the ring is made of a material that allows the slots to be "closed" to permit the passage of magnetic flux when the stator winding is not energized, and to be "opened" when a relatively high current flows through the winding to prevent the passage of magnetic flux, particularly in a circumferential direction around the ring. Thus, the ring reduces the variation in the magnetic permeability of the air gap between the rotor and the stator.

[0010] Furthermore, under normal machine operating conditions, the invention makes it possible to obtain air gap permeability similar to that in a machine with closed slots towards the air gap as described above, but unlike such a machine, the invention avoids winding the stator from the outside. Consequently, it is possible to use a segmented stator formed by stator sectors in order to increase the filling ratio of the electrical conductors. The invention makes it possible to avoid changing the conventional machine manufacturing procedure, such as the winding process. Also, The invention allows the use of magnetic shims, which is difficult in a segmented or small-sized stator.

[0011] By "normal operating conditions of the machine," it is understood that the machine is not stopped. In particular, the machine current may be greater than 50% of the motor's rated current. For example, the machine may operate at its rated voltage and power. The voltage may be between 0 and 1000 V and the power may be between 0 and 20 kW.

[0012] The ring can be made of a material that saturates rapidly when the magnetic flux increases in the machine. When there is no current in the stator winding, the magnetic flux can pass through the magnetic ring. Under load conditions, since the ring's thickness is very small, it saturates quickly. Therefore, the stator functions as a closed-slot stator.

[0013] The ring can saturate to prevent the passage of a magnetic flux, in particular in a circumferential direction of the magnetic ring, particularly when the machine current is greater than 50% of the motor's nominal current.

[0014] The ring thickness can be between 0.1 and 1 mm, or even between 0.2 mm and 0.8 mm, preferably between 0.3 and 0.5 mm. The air gap thickness between the rotor and the stator can be between 0.2 and 2 mm before the ring is installed. This thickness can be between 0.1 and 1 mm after the ring is installed.

[0015] The magnetic ring can be continuous, in particular monobloc.

[0016] The rotor can be made of permanent magnets. The rotor can be located radially inside the stator, for example around an axis of rotation of the machine.

[0017] The stator may include a stator mass. Slots may be formed in the stator mass, oriented longitudinally along the machine. The stator mass may have a central opening, and the slots may be oriented towards this central opening. The rotor may be located within the central opening. The air gap between the stator and the rotor may, for example, have a thickness of between 0.1 and 2 mm, or even between 0.2 and 1 mm, preferably between 0.3 and 0.6 mm. The thickness of the air gap may be measured in the presence of the magnetic ring.

[0018] By a machine or stator with open slots or an open contour towards the air gap between the rotor and the stator, it must be understood that the contour of the stator slots is not closed by the stator mass material on the air gap side, unlike a machine or stator with closed slots or a closed contour towards the air gap between the rotor and the stator. Thus, the slots have openings towards the air gap between the rotor and the stator. The stator according to the invention is free of magnetic shims inserted in the slot openings towards the air gap. The slot openings may have a dimension e, measured in a direction circumferential of the stator, less than 3 mm, or even less than 2.5 mm, preferably less than 2 mm. The openings of the slots may have a dimension e, measured in a circumferential direction of the stator, greater than 0.5 mm, or even greater than 1 mm, preferably greater than 1.5 mm.

[0019] The stator may have teeth formed between the notches. The teeth may be connected to each other on the side opposite the air gap by a yoke. Preferably, at least one tooth is integral with at least a portion of the yoke. For example, the yoke is integral with the teeth.

[0020] The stator mass can be made by stacking magnetic laminations. The slots can be formed by cutting the laminations. Each lamination in the stack can be a single piece. The stator mass is, for example, made by stacking magnetic steel laminations, for example, steel 0.1 to 1.5 mm thick, having a permeability of approximately 4000 times that of free space, the permeability of free space being 4π × 10⁷ H / m. The laminations can be coated with an electrically insulating varnish on their opposite faces before being assembled in the stack. Electrical insulation can also be obtained by heat-treating the laminations, if necessary.

[0021] The stator mass can be segmented, that is, comprised of added stator sectors. The sectors are, for example, formed by cutting. Each sector can comprise a stator tooth. A stator sector can comprise at least one tooth and a portion of the yoke. For example, a sector can comprise a single tooth and a portion of the yoke. A stator sector is, for example, a single piece or, alternatively, made by stacking sectors of magnetic laminations. The sectors can be connected to each other in a circumferential direction of the stator. A notch is formed between two consecutive sectors.

[0022] In one embodiment, the stator mass is produced at least partially by an additive manufacturing technique, in particular by powder sintering and machining. The stator may comprise a plurality of stacked wafers, each produced by additive manufacturing.

[0023] The relative permeability of the magnetic ring material with respect to air or vacuum can be greater than 2, or even greater than 3, and in particular greater than 5. The permeability of vacuum or air is 4ir*10⁷ H / m. For example, a material having a relative permeability of 5 means that the permeability of this material is 5*4ir*10⁷ H / m.

[0024] The relative permeability of the magnetic ring material with respect to the stator mass may be less than 1 / 2000, or even less than 1 / 200, in particular less than 1 / 20.

[0025] The choice of the relative permeability of the magnetic ring material is, in particular, a compromise between reducing the rattling effect and reducing the machine's rated torque. For example, a material with high relative permeability can significantly reduce the rattling effect, but at the same time, the machine's rated torque may also decrease considerably.

[0026] The magnetic ring can be made with a material comprising iron powder, epoxy resin and glass fibers, in particular with a material comprising at least, or even solely, iron powder, epoxy resin and glass fibers.

[0027] The material may comprise, for example, between 50% and 90% iron powder, or even between 60% and 80%, for example about 70%.

[0028] The material may comprise between 5% and 40% epoxy resin, for example between 10% and 30%, in particular about 20%.

[0029] The material may comprise between 5 and 20% glass fibers, for example between 5% and 15%, in particular about 10%.

[0030] The magnetic ring may have a radially outer surface in contact with the inner surface of the stator, this radially outer surface of the magnetic ring being, for example, smooth.

[0031] In one embodiment, the radially outer surface of the magnetic ring has protrusions. The stator may have notches located on the surface of the teeth facing the air gap. The protrusions on the radially outer surface of the magnetic ring are, for example, received in the notches. In one embodiment, each tooth has a notch on the inner surface of the stator. The notch may be centered with respect to the corresponding tooth.

[0032] In another embodiment, the radially outer surface of the magnetic ring has notches. The stator may have protrusions located on the surface of the teeth towards the air gap. The protrusions of the stator are, for example, received in the notches of the radially outer surface of the magnetic ring.

[0033] The notches and / or protrusions may have a rectangular, semi-circular or trapezoidal shape.

[0034] The magnetic ring can be attached to the stator by an insulating material, in particular an epoxy resin, specifically the insulating material used to attach the electrical conductors to the stator ground. In one embodiment, the magnetic ring is attached to the stator ground during a step of impregnating the stator winding. For example, the stator winding can be completely impregnated with an insulating material such as a resin, in particular an epoxy resin, or a varnish. This material is injected into the machine and then cured or polymerized to bond the winding to the stator ground. The magnetic ring can be attached to the ground stator during this step of impregnating the stator winding with this insulating material. In a variant, the ring can be fixed to the stator ground by gluing.

[0035] The electrical conductors are, for example, arranged in a concentrated or distributed manner within the slots. "Concentrated" means that the electrical conductors are arranged around a single tooth. "Distributed" means that the starting and returning electrical conductors are housed in different, non-consecutive slots. At least one of the electrical conductors may pass successively through two non-adjacent slots. Preferably, the electrical conductors are arranged in a distributed manner within the slots.

[0036] The stator may have an internal diameter of less than 150 mm, or even less than 100 mm, better less than 70 mm.

[0037] According to another aspect, the invention relates to a method for manufacturing a rotating electrical machine, in which a stator mass having a central opening is made, notches being formed through the stator mass in a longitudinal direction of the machine, the notches having openings towards the central opening, method in which a magnetic ring is disposed in the central opening in contact with the stator mass, in particular in contact with an internal surface of the stator mass defining the central opening.

[0038] The stator mass can be made by stacking magnetic laminations, with the slots formed by cutting the laminations. The stator mass may include attached stator sectors. In one embodiment, the stator mass is at least partially produced by an additive manufacturing technique, in particular by powder sintering and machining.

[0039] The stator mass can be wound through the openings of the slots.

[0040] The magnetic ring can be fixed to the stator mass during a step of impregnating the stator winding, in particular by means of a resin, in particular an epoxy resin.

[0041] According to another aspect, the invention also relates to a surgical robot comprising a rotating electrical machine as described above. The invention makes it possible to improve the smoothness of the robot's operation. Brief description of the drawings

[0042] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the accompanying drawing on which:

[0043] [Fig-1] Fig. 1 is a schematic and partial cross-sectional view of a rotating electric machine according to the invention.

[0044] [Fig.2] The [Fig.2] is a schematic and partial perspective view of a stator sector.

[0045] [Fig.3] Fig.3 represents the variation in permeability of a material for the magnetic ring.

[0046] [Fig.4] The [Fig.4] is a schematic and partial cross-sectional view of an alternative embodiment. Detailed description

[0047] Figure 1 illustrates a rotating electrical machine comprising a rotor 1 and a stator 2. The machine is a synchronous machine. For example, the machine is a motor. The rotor 1 has permanent magnets, which are arranged on the surface of the rotor mass.

[0048] In the illustrated embodiment, the stator 2 has a central opening 28. The rotor 1 is located in the central opening. An air gap 23 is formed between the rotor 1 and the stator 2. The central opening 28 can define an internal diameter d of the stator. The internal diameter d is, for example, less than 70 mm.

[0049] The stator 2 comprises a stator mass 20. The stator mass has teeth 27 and slots 21 formed between the teeth 27. The slots 21 are open towards the air gap 23. In other words, two adjacent teeth 27 defining a slot 21 are not connected to each other on the side of the air gap 23. Each slot 21 has an opening 25 towards the air gap 23. These openings have, for example, a dimension e, measured in a circumferential direction of the stator, of less than 3 mm. However, the invention can be applied to openings of a different dimension. The teeth 27 have polar flares 26 on the side of the air gap 23.

[0050] On the side opposite the air gap 23, two adjacent teeth 27 of the stator mass 20 are connected to each other by a yoke 29. In the case of a segmented stator comprising stator sectors 200, the yoke 29 can be a single piece with one tooth 27 in each magnetic lamination forming a sector 200, as illustrated in [Fig. 2]. When the sectors 200 are connected to each other, a notch 21 is formed between the teeth 27 of two adjacent sectors 200. In the case of a non-segmented stator formed by a stack of stator laminations, the yoke 29 can be a single piece and comes as a single unit with all the teeth 27 within each lamination.

[0051] At least one notch 21, or preferably all the notches 21, may have a generally trapezoidal cross-section. At least one notch, or preferably all the notches, may have diverging edges when viewed from away from the axis of rotation X of the machine.

[0052] At least one tooth 27, preferably all teeth 27, may have a generally rectangular cross-section. At least one tooth may have opposing radial edges. at least partially parallel to each other; better still, all teeth should have radial edges that are at least partially parallel to each other. The width of a tooth is preferably substantially constant over most of its height.

[0053] A magnetic ring 3 is disposed in the air gap 23 between the rotor 1 and the stator 2. The ring 3 is disposed against an internal surface 22 of the stator mass 20. The ring 3 is in contact with the stator mass 20 on the internal surface 22 thereof.

[0054] The ring 3 is made of a material whose relative magnetic permeability with respect to the magnetic steel constituting the stator mass decreases rapidly with increasing magnetic field density. An example of such a material is composed of 70% iron powder, 20% epoxy resin, and 10% glass fabric. Figure 3 illustrates the relative magnetic permeability of this material as a function of the magnetic field density B in Tesla.

[0055] The ring dimensions can also be chosen such that the ring saturates rapidly when the magnetic flux increases in the machine. The ring thickness in the radial direction is less than 1 mm. However, to ensure sufficient mechanical strength, the ring thickness 3 is preferably greater than 0.3 mm. The choice of ring thickness 3 may also depend on the magnetic properties of the ring material. A large thickness may lead to a reduction in the machine's rated torque density.

[0056] In the embodiment of [Fig.1], a radially outer surface 37 of the magnetic ring 3 in contact with the inner surface 22 of the stator is smooth.

[0057] In the embodiment illustrated in [Fig. 4], the radially outer surface 37 of the magnetic ring 3 has protrusions 34. The stator has notches 24 on its inner surface 22, located on the surface of the teeth towards the air gap 23. The protrusions 34 are received in the notches 24. In the illustrated embodiment, each tooth 27 has a notch 24 on its radially inner surface forming part of the inner surface 22 of the stator mass 20. This ring shape 3 of the protrusions 34 further reduces the engagement torque. The dimensions of the notches 24 are substantially identical or slightly greater than those of the protrusions 34 in order to reduce the gap between the notches 24 and the protrusions 34 when the protrusions 34 are received in the notches 24. The notches 24 and / or the protrusions 34 preferably have a rectangular or semi-circular or trapezoidal shape.

[0058] The electrical conductors (not shown) can be wound around the teeth 27 in the notches 21. The electrical conductors can be arranged in the notches 21 in a concentrated or distributed manner.

[0059] The electrical conductors may be conducting wires. In one embodiment, the electrical conductors may be in the form of pins. The pin may be U-shaped (or "U-pin") or straight, being I-shaped (or "1-pin"). The electrical conductors are preferably made of copper or aluminum.

[0060] The electrical conductors can be electrically insulated from the outside by an insulating coating, in particular an enamel or an epoxy resin. The electrical conductors can be separated from the walls of the slot by an insulator, in particular by at least one sheet of insulator. Such a sheet insulator provides better insulation of the electrical conductors from the stator mass.

[0061] The invention is not limited to the embodiment described. For example, the invention can be combined with a skewed stator, for example, in order to further reduce the notching effect.

Claims

Demands

1. Rotating electrical machine comprising a rotor (1) and a stator (2), the stator (2) having slots (21) in which electrical conductors are housed, the slots (21) being open towards an air gap (23) provided between the rotor and the stator, the machine comprising a magnetic ring (3) located in the air gap (23) in contact with an internal surface of the stator, the magnetic ring (3) having a permeability configured to prevent the passage of a magnetic flux under normal operating conditions of the machine, in particular in a circumferential direction of the magnetic ring (3).

2. Machine according to the preceding claim, the stator (2) comprising a stator mass (20), the magnetic ring (3) comprising a material having a relative permeability with respect to air or vacuum greater than 2, or even greater than 3, in particular greater than 5.

3. Machine according to any one of the preceding claims, the magnetic ring (3) being continuous, in particular monobloc.

4. Machine according to any one of the preceding claims, the notches (21) having openings (25) to the air gap (23), these openings (25) having a dimension (e), measured in a circumferential direction of the stator, of less than 3 mm.

5. Machine according to any one of the preceding claims, the thickness of the ring being between 0.1 and 1 mm, or even between 0.2 and 0.8 mm, better between 0.3 and 0.5 mm.

6. Machine according to any one of the preceding claims, the magnetic ring saturating to prevent the passage of a magnetic flux, in particular in a circumferential direction of the magnetic ring (3), when the machine current is greater than 50% of the motor's rated current.

7. Machine according to any one of the preceding claims, the magnetic ring being made with a material comprising iron powder, epoxy resin and glass fibers.

8. Machine according to any one of the preceding claims, the magnetic ring being fixed to the stator by an insulating material, in particular an epoxy resin, in particular the insulating material used to fix the electrical conductors to the stator mass (20) of the stator (2).

9. Machine according to any one of the preceding claims, the magnetic ring having a radially outer surface (37) in contact with the inner surface of the stator, the radially outer surface (37) of the magnetic ring (3) being smooth.

10. Machine according to any one of claims 1 to 8, the magnetic ring having a radially outer surface (37) in contact with the inner surface of the stator, the radially outer surface of the magnetic ring (3) having protrusions (34).

11. Machine according to the preceding claim, the stator having teeth (27) formed between the notches (21), the stator having notches (24) located on the surface of the teeth (27) towards the air gap (23), the protrusions (34) being received in the notches (24), each tooth having in particular a notch (24) on the internal surface of the stator, the notch being in particular centered with respect to the corresponding tooth.

12. Method of manufacturing a rotating electrical machine, in which a stator mass (20) having a central opening (28) is made, notches (21) being formed through the stator mass (20) in a longitudinal direction of the machine, the notches (21) having openings (25) towards the central opening (28), method in which a magnetic ring (3) is disposed in the central opening (28) in contact with the stator mass (20).

13. Method of manufacturing a rotating electrical machine according to the preceding claim, the stator mass (20) being wound through the openings (25) of the slots (21).

14. A manufacturing method according to the preceding claim, the magnetic ring (3) being fixed to the stator mass (20) during an impregnation step of the stator winding (2), in particular by means of a resin, in particular an epoxy resin.

15. Surgical robot comprising a rotating electrical machine according to any one of claims 1 to 11.

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