Rotor structure corresponding to servo motor

Abstract

The utility model relates to a rotor structure corresponding to a servo motor. The rotor structure comprises a rotor core and a permanent magnet, the rotor iron core is uniformly divided into a plurality of magnetic poles along the circumferential direction; the magnetic poles are symmetric about a midline d; the magnetic pole is provided with a pair of magnet grooves which are in V-shaped symmetry based on the center line, and a pair of permanent magnets are arranged in the magnet grooves respectively. Along the clockwise direction, the arc edge of the magnetic pole is composed of a plurality of stepped discontinuous arcs which sequentially comprise a first arc, a second arc, a third arc, a fourth arc and an arc symmetric about the d axis of the first arc, the second arc and the third arc. Through discontinuous arcs, uneven air gaps are formed between a stator and a rotor, the harmonic content of counter electromotive force is reduced, cogging torque and torque pulsation are reduced, and the control precision and the stability of motor output torque are improved; meanwhile, harmonic loss is reduced, rotor temperature rise is reduced, and motor efficiency is improved; uneven air gaps are equivalent to weight reduction on the outer circle of the rotor; in combination with the lightening holes, the rotational inertia of the rotor is greatly reduced, and the response speed of the motor is improved.

Description

Technical Field

[0001] The invention relates to a rotor structure, in particular to a rotor structure corresponding to a servo motor, and belongs to the technical field of industrial motors. Background Art

[0002] At present, permanent magnet synchronous servo motors are widely used in some high-precision transmission fields of industrial automation. They rely on adding permanent magnets to the rotor to generate a permanent magnetic field. Compared with traditional asynchronous motors, they have the advantages of high power factor, high efficiency, wide speed regulation range, simple structure, small size, and reliable operation. They have been widely used in CNC machine tools, robots and other occasions.

[0003] Traditional servo motor rotors are divided into surface-mount and embedded types according to the position of the permanent magnet.

[0004] The permanent magnets of the surface-mounted rotor are directly attached to the outer circle of the rotor core and generally require a sleeve to fix them. Therefore, the air gap between the stator and rotor needs to be designed to be larger. At the same time, since the dq axis inductance of this structure is equal, the reluctance torque cannot be used to improve the output performance of the motor, resulting in a low torque density of the motor, a large volume at the same power, a large amount of material consumption, high cost, and poor economy.

[0005] The permanent magnets of the embedded rotor are embedded in the magnetic steel slots of the iron core, which are mainly divided into "I"-shaped embedded and "V-shaped embedded". The "I"-shaped embedded magnetic pole has no magnetic concentration effect, and the utilization rate of the magnetic resistance torque is low. It is mainly used in occasions where the power density requirement is not high. The "V"-shaped magnetic pole structure process is relatively simple, and it has a magnetic concentration effect. At the same time, the cross-axis loop channel is widened, which can improve the magnetic resistance torque. The outer circle of the traditional "V"-shaped magnetic pole is a full circle, and the air gap is uniform on the circumference. Such a design is not easy to weaken the back electromotive force harmonic content, and the sinusoidality of the air gap magnetic density waveform is poor, which increases the tooth torque and torque pulsation, which is not conducive to servo control and reduces the control accuracy; at the same time, the increase in harmonic content will also lead to more harmonic losses, increased rotor heating, and reduced motor efficiency, affecting the output performance of the motor, especially for integer slot motors, which often need to be improved by means of skewed slots or skewed poles, which increases the process difficulty and manufacturing cost. In addition, the outer circle of the traditional "V"-shaped magnetic pole rotor is a full circle (such as Figure 1 The weight-reducing holes are usually opened near the rotating shaft, which has limited effect on improving the moment of inertia. The moment of inertia of the motor directly affects the response speed of the motor, so it is not suitable for occasions that require fast response. Summary of the invention

[0006] In order to solve the deficiencies of the prior art, an object of the present invention is to provide a rotor structure corresponding to a servo motor.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A rotor structure comprises a rotor core and a permanent magnet; the rotor core is divided into a plurality of magnetic poles along the circumferential direction; the magnetic poles are symmetrical based on a midline d axis;

[0009] The magnetic pole is provided with a pair of magnet slots which are V-shaped and symmetrical based on the midline, and a pair of permanent magnets are respectively placed in the magnet slots;

[0010] In the clockwise direction, the arc edge of the magnetic pole is composed of a plurality of discontinuous arcs in a stepped shape, including, in sequence, a first arc (41), a second arc (42), a third arc (43), a fourth arc (44), and three other arcs symmetrical to the first, second and third arcs about the d axis;

[0011] The center of the first arc (41) is the center point O of the rotor core, the radius is R2, and the center angle is α1;

[0012] The centers of the second arc (42), the third arc (43) and the fourth arc (44) are point O' on the midline, and the radii are R3, R4 and R5 respectively;

[0013] The center angles of the second arc (42), the third arc (43) and the fourth arc (44) based on the center point O are α2, α3 and β respectively.

[0014] in, R3<R4,R4<R5, α2>0,α3>0,

[0015] 0.15R1≤H1≤0.3R1, R5=R1-H1, 0.6θ≤β≤σ*θ;

[0016] Where R1 is the outer diameter of the rotor core, H1 is the distance between OO', θ is the central angle of the rotor core occupied by the magnetic pole, θ = 360° / 2P, P is the number of pole pairs of the motor, and σ is the pole arc coefficient of the magnetic pole.

[0017] The first arc is directly connected to the second arc, and the second arc is connected to the third arc, and the third arc is connected to the fourth arc by a smooth straight line that forms an angle γ with the center line of the magnetic pole, 30°<γ<45°, and a chamfered transition is set at each arc or at the connection between the arc and the straight line, and the rounded corners are uniformly recorded as Ra, Ra=0.2~0.5mm.

[0018] The thickness of the permanent magnet is L3, the angle formed between the magnet slots is △, there is a magnetic isolation bridge between the magnet slots, and the width of the magnetic isolation bridge is L4, wherein σ*180°-20°<△<σ*180°+20°, L4=0.8mm~1.5mm.

[0019] The rotor core is provided with a weight-reducing hole between the magnet slot and the shaft hole;

[0020] The weight-reducing holes are evenly distributed along the circumferential direction, the number of the weight-reducing holes is the same as the number of magnetic poles, and the center lines of the weight-reducing holes coincide with the q-axis of the magnetic poles; adjacent weight-reducing holes are symmetrical based on the d-axis.

[0021] Furthermore, the above-mentioned weight-reducing holes are pentagonal in shape, wherein:

[0022] The two sides are parallel to the d-axis, and the shortest distance between two adjacent weight-reducing holes is L1;

[0023] The two top edges are parallel to the bottom edges of the adjacent magnet slots, with a distance of L2;

[0024] The inner side is an arc with the center at point O and a radius of R7, where L1 = (0.5-1)*(n / 10000) 3 *R1, n is the maximum speed of the motor, unit rpm; L2 = (2.5L3 ~ 3.5L3); R7 = R6 + (0.25 ~ 0.5) * (n / 10000) 3 *R1.

[0025] The number of the magnetic poles is 8.

[0026] The first arc, the second arc and the third arc are all straight lines.

[0027] An industrial servo motor comprises the above-mentioned rotor structure.

[0028] The present invention is beneficial in that:

[0029] A rotor structure and an industrial servo motor of the present invention are provided with multiple discontinuous arcs in a stepped shape on the outer circumference of the rotor core, and are symmetrical based on the d axis, thereby forming an uneven air gap between the stator and the rotor, which greatly reduces the harmonic content of the back electromotive force, reduces the cogging torque and torque pulsation, and improves the control accuracy and the stability of the motor output torque; at the same time, the harmonic loss is reduced, the rotor temperature rise is reduced, and the motor efficiency is improved; and the uneven air gap is equivalent to a weight reduction design on the outer circumference of the rotor; combined with the weight reduction holes, the moment of inertia of the rotor is greatly reduced, the response speed of the motor is improved, and the problem of poor motor response speed in the prior art is improved;

[0030] The rotor structure and industrial servo motor of the present invention solve the problems of high back-EMF harmonic content, poor servo control accuracy, large harmonic loss, low efficiency and the like of permanent magnet motors in the prior art by cleverly optimizing the design of the rotor structure; there is no need to use skewed slots or skewed poles, which reduces the difficulty of process production and manufacturing costs, improves the production efficiency of the motor, and has strong practicality and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the magnetic pole.

[0032] Figure 2 Dimensioning diagram for magnetic poles.

[0033] Figure 3 Schematic diagram of the stator and rotor structure of an industrial servo motor.

[0034] Figure 4 for Figure 3 A partial enlarged view of point A in the middle.

[0035] Figure 5 A comparison diagram of back EMF waveforms between the technology of the present invention and the prior art;

[0036] Figure 6 A comparison diagram of torque and torque fluctuation between the technology of the present invention and the prior art

[0037] The reference numerals are as follows: 1. magnetic pole, 11, 12, 13. magnetic isolation bridge, 2. magnet slot, 3. permanent magnet, 41. first arc, 42. second arc, 43. third arc, 44. fourth arc, 5. weight-reducing hole, 6. shaft hole. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] A servo motor includes the following rotor structure.

[0040] The rotor structure consists of a rotor core and permanent magnets.

[0041] The outer diameter of the rotor core is R1, the center of the circle is point O, and an axial hole is provided at the center of the circle, and the radius of the axial hole is R6. Along the circumferential direction, the rotor core is evenly divided into a number of magnetic poles; the central angle occupied by each magnetic pole is θ, θ=360° / 2P, and P is the number of pole pairs of the motor. Preferably, the number of magnetic poles is 8.

[0042] like Figure 1 As shown,

[0043] The symmetric center line of the magnetic pole is the d-axis. On the outer circumference of the rotor core, the arc edge of the magnetic pole is composed of multiple discontinuous arcs in a stepped shape. In the clockwise direction, the arc edge is composed of the first arc 41, the second arc 42, the third arc 43, the fourth arc 44 and another three arcs that are symmetrical about the d-axis.

[0044] like Figure 2 As shown,

[0045] The center of the first arc 41 coincides with the center of the rotor core, the radius is R2, and the center angle is α1.

[0046] The fourth arc 44 has its center at point O', its corresponding center angle at angle β, and its radius at R5, wherein the distance between OO' is H1, and 0.15R1≤H1≤0.3R1, R5=R1-H1, 0.6θ≤β≤σ*θ, where σ is the pole arc coefficient of the rotor magnetic pole.

[0047] The center of the second arc 42 and the third arc 43 is point O', the angles formed by the lines connecting the start and end points of the two arcs and the center point O are α2 and α3 respectively, the radius of the second arc is R3, and the radius of the third arc 43 is R4, wherein R3<R4,R4<R5, α2>0,α3>0,

[0048] The first arc 41 is directly connected to the second arc 42, and the second arc 42 and the third arc 43, as well as the third arc 43 and the fourth arc 44 are connected by a smooth straight line that forms an angle γ with the magnetic pole d axis, wherein 30°<γ<45°, and a chamfered transition is set at the connection between each arc or the arc and the straight line, and the rounded corner is uniformly denoted as Ra, Ra=0.2~0.5mm.

[0049] The magnetic pole is provided with a pair of magnet slots that are V-shaped and symmetrical based on the d-axis, and a pair of permanent magnets are placed in the magnet slots. The thickness of the permanent magnet is L3, the angle formed between the magnet slots is △, there is a magnetic isolation bridge between the magnet slots, and the width of the magnetic isolation bridge is L4, where σ*180°-20°<△<σ*180°+20°, L4=0.8mm~1.5mm. By constraining the topological structure of the rotor, the harmonic content and torque fluctuation of the back electromotive force can be reduced while ensuring the strength of the rotor, thereby improving the output torque and torque stability of the motor.

[0050] A plurality of weight-reducing holes 5 are provided on the rotor core between the magnet slots and the shaft holes. The weight-reducing holes are evenly distributed along the circumferential direction, and the number of the weight-reducing holes is the same as the number of magnetic poles. The center line of the weight-reducing holes coincides with the q-axis of the magnetic poles. Adjacent weight-reducing holes are symmetrical based on the d-axis.

[0051] The shape of the weight-reducing hole is similar to a pentagon. The left and right sides (two sides) of the weight-reducing hole are parallel to the d-axis. The shortest distance between the two weight-reducing holes is L1. The upper left and upper right sides (two top sides) of the weight-reducing hole are respectively parallel to the bottom sides of the two magnet slots, and the straight-line distance is L2. The radial inner side of the weight-reducing hole is an arc with the center at point O and a radius of R7, where L1 = (0.5-1)*(n / 10000) 3*R1, n is the maximum speed of the motor, unit rpm; L2 = (2.5L3 ~ 3.5L3); R5 = R6 + (0.25 ~ 0.5) * (n / 10000) 3 *R1. The weight reduction design of the weight reduction hole can reduce the weight of the rotor to the greatest extent without affecting the electromagnetic performance and mechanical strength; coupled with the design of the uneven air gap at the outer circle of the rotor, according to the formula of the moment of inertia ω=mr 2 It can be seen that the farther the weight is from the center of the rotor, the smaller the weight is, and the more obvious the reduction in rotational inertia is. The lower the rotational inertia, the better the response speed of the motor will be, and smooth control and small oscillation can be achieved in the entire speed range.

[0052] like Figure 3 and Figure 4 As shown, the air gap between the stator and the rotor increases first and then decreases from the d-axis to the q-axis and then to the d-axis. The air gap is the largest at the q-axis and the smallest at the d-axis, and it changes alternately in a periodic manner. Compared with the traditional uniform air gap, this design greatly weakens the harmonic content of the back electromotive force and makes the waveform of the air gap magnetic field more sinusoidal.

[0053] like Figure 5 and 6 The figure shows the comparison of back EMF waveform and torque between the prior art and the technology of the present invention, wherein the back EMF harmonic content of the prior art is 16.3% at most, and the torque fluctuation is 10%; the back EMF harmonic content of the present invention is only 3%, and the torque fluctuation is 2%, which are reduced by 81.6% and 80% respectively compared with the prior art, and the improvement effect is significant.

[0054] Low harmonic content can reduce cogging torque, reduce torque fluctuation, and make the output torque of the motor more stable, thereby improving the vibration and noise of the motor, extending the service life of the industrial motor, and improving the customer experience.

[0055] Reducing the harmonic content of back EMF can also reduce the losses caused by current harmonics, reduce rotor heating, lower the operating temperature of permanent magnets, and reduce the risk of permanent magnet demagnetization; in addition, the stator current of the motor will be reduced at the same output power, and the copper loss of the motor will be reduced, thereby improving the efficiency of the motor.

[0056] It has been verified that the size of the air gap near the q-axis is more sensitive to back-electromotive force harmonics and torque fluctuations, but an excessively large air gap will cause a great loss of motor torque. Therefore, the present invention uses a stepped arc near the q-axis to construct an uneven air gap. The farther away from the q-axis, the smaller the air gap. On the one hand, it can reduce harmonics, and on the other hand, it can maximize the output torque of the motor to ensure the performance of the motor.

[0057] The present invention limits the central angle of the first arc The second arc and the third arc, and the third arc and the fourth arc are connected by a smooth straight line that forms an angle γ with the magnetic pole d axis, wherein 30°<γ<45°, ensuring that the magnetic isolation bridge 12 and the magnetic isolation bridge 13 have equal thickness in the circumferential direction, which can reduce rotor leakage and improve the motor output capacity, while reducing rotor stress and ensuring that the motor reaches a higher speed.

[0058] In the prior art, in order to weaken the back EMF harmonics, reduce the cogging torque and torque fluctuation, the method of slanted poles or slanted slots is often used, which requires staggered pole design in structure, and also requires segmented slanted pole assembly or design and manufacture of corresponding tooling in production and process, which increases the process and assembly difficulty and reduces production efficiency. The structure of the present invention greatly simplifies the manufacturing process of the stator and rotor and improves production efficiency.

[0059] In addition, in the present invention, for the sake of process simplicity, the first arc, the second arc and the third arc can also be replaced by smooth straight lines with similar effects, which can also reduce back-electromotive force harmonics, reduce cogging torque and reduce torque ripple.

[0060] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A rotor structure corresponding to a servo motor, characterized in that: It includes a rotor core and a permanent magnet; along the circumferential direction, the rotor core is evenly divided into a plurality of magnetic poles; the magnetic poles are symmetrical based on the center line d; The magnetic pole is provided with a pair of magnet slots which are V-shaped and symmetrical based on the midline, and a pair of permanent magnets are respectively placed in the magnet slots; In the clockwise direction, the arc edge of the magnetic pole is composed of a plurality of discontinuous arcs in a stepped shape, including, in sequence, a first arc (41), a second arc (42), a third arc (43), a fourth arc (44), and three other arcs symmetrical to the first, second and third arcs about the d axis; The center of the first arc (41) is the center point O of the rotor core, the radius is R2, and the center angle is α1; The centers of the second arc (42), the third arc (43) and the fourth arc (44) are point O' on the midline, and the radii are R3, R4 and R5 respectively; The center angles of the second arc (42), the third arc (43) and the fourth arc (44) based on the center point O are α2, α3 and β respectively. in, R3<R4,R4<R5, α2>0,α3>0, 0.15R1≤H1≤0.3R1, R5=R1-H1, 0.6θ≤β≤σ*θ; Where R1 is the outer diameter of the rotor core, H1 is the distance between OO', θ is the central angle of the rotor core occupied by the magnetic pole, θ = 360° / 2P, P is the number of pole pairs of the motor, and σ is the pole arc coefficient of the magnetic pole.

2. The rotor structure according to claim 1, characterized in that: The first arc is directly connected to the second arc, and the second arc is connected to the third arc, and the third arc is connected to the fourth arc by a smooth straight line that forms an angle γ with the center line of the magnetic pole, 30°<γ<45°, and a chamfered transition is set at each arc or at the connection between the arc and the straight line, and the rounded corners are uniformly recorded as Ra, Ra=0.2~0.5mm.

3. The rotor structure according to claim 1, characterized in that: The thickness of the permanent magnet is L3, the angle formed between the magnet slots is △, there is a magnetic isolation bridge between the magnet slots, and the width of the magnetic isolation bridge is L4, wherein σ*180°-20°<△<σ*180°+20°, L4=0.8mm~1.5mm.

4. The rotor structure according to claim 1, characterized in that: The rotor core is provided with a weight-reducing hole between the magnet slot and the shaft hole; The weight-reducing holes are evenly distributed along the circumferential direction, the number of the weight-reducing holes is the same as the number of magnetic poles, and the center lines of the weight-reducing holes coincide with the q-axis of the magnetic poles; adjacent weight-reducing holes are symmetrical based on the d-axis.

5. The rotor structure according to claim 4, characterized in that: The weight-reducing holes are pentagonal in shape, wherein: The two sides are parallel to the d-axis, and the shortest distance between two adjacent weight-reducing holes is L1; The two top edges are parallel to the bottom edges of the adjacent magnet slots, with a distance of L2; The inner side is an arc with the center at point O and a radius of R7, where L1 = (0.5-1)*(n / 10000) 3 *R1, n is the maximum speed of the motor, unit rpm; L2 = (2.5L3 ~ 3.5L3); R7 = R6 + (0.25 ~ 0.5) * (n / 10000) 3 *R1, R6 are the radii of the rotor core shaft hole.

6. The rotor structure according to claim 1, characterized in that: The number of magnetic poles is 8.

7. The rotor structure according to claim 1, characterized in that: The first arc, the second arc and the third arc are all straight lines.

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