Linear actuator

Abstract

The invention provides a linear actuator which comprises a base assembly, a first stator iron yoke is arranged at the top end of the base assembly, a second stator iron yoke is coaxially arranged at the top end of the first stator iron yoke, the bottom of the second stator iron yoke is provided with a containing cavity and an annular cavity, the containing cavity and the annular cavity are coaxial, a hole is formed in the top end of the containing cavity, a coaxial boss is arranged at the top end of the second stator iron yoke, and coaxial actuating magnetic steel is arranged on the inner circumferential wall of the annular cavity; an air floater is arranged at the bottom end of the top sealing assembly, and the air floater is arranged on the outer side of the second stator iron yoke in a sleeving mode; the coil framework is fixed to the bottom end of the top sealing assembly and located on the inner side of the air floater, an actuating coil and compensation magnetic steel which are coaxial are sequentially arranged on one side, from outside to inside, of the bottom end of the coil framework in the radial direction, the actuating coil enters the annular cavity along a hole in the top end of the annular cavity, and the compensation magnetic steel enters the containing cavity along a hole in the top end of the containing cavity; and the annular air floatation stator is arranged at the top end of the first stator iron yoke and sleeves the outer side of the air floatation stator, and a plurality of vent holes are formed in the outer wall of the annular air floatation stator. The device has the beneficial effects that the load capacity can be improved, and the working stroke can be adaptively adjusted.

Description

Technical Field

[0001] The present invention relates to the technical field of linear actuation motors, and in particular to a linear actuator. Background Art

[0002] With the rapid development of humanoid robotics, the performance requirements for linear actuators in their joint drive systems are increasing. Core actions such as telescopic movement of robotic arms and finger grasping require not only precise displacement control capabilities but also special requirements such as high power density, fast response, and compact structure. Currently, mainstream linear motion implementation methods are categorized as mechanical transmission, fluid drive, and electromagnetic direct drive. However, these methods all face significant technical bottlenecks in practical applications.

[0003] Traditional mechanical transmission solutions are typically based on a "rotating motor + screw mechanism" combination, typically categorized into two types: ball screws and planetary roller screws. Ball screws achieve transmission through the rolling friction of circulating balls between the screw and nut, offering transmission efficiency exceeding 90% and positioning accuracy up to ±5μm. However, they suffer from difficulties in eliminating axial clearance and weak resistance to shock loads. Planetary roller screws utilize a multi-threaded meshing structure, which increases load capacity to 3-5 times that of ball screws. However, transmission efficiency drops to 60-70%, and precision machining significantly increases manufacturing costs. More critically, this type of two-stage transmission system requires auxiliary components such as reducers and couplings, increasing the overall axial length by over 40%, making it difficult to meet the compact design requirements of humanoid robot joint modules.

[0004] Fluid drive solutions primarily include hydraulic pistons and pneumatic pistons. Hydraulic systems, leveraging the Pascal principle, can achieve operating pressures up to 35 MPa, and a single-stage transmission can generate several tons of thrust output. However, these systems have inherent drawbacks: First, the viscosity-temperature characteristics of hydraulic oil limit system response speed. At -20°C, response delays can reach 2-3 times that of normal temperature. Second, the manufacturing costs of precision servo valves and high-pressure seals account for over 60% of the total system cost. Furthermore, the complexity of the piping layout makes modular integration of the system difficult. While pneumatic drive offers the advantages of cleanliness and environmental protection, its position control accuracy is typically limited to ±1 mm due to the compressibility of the gas, and its maximum thrust is limited to less than 500 N, making it unable to meet the load requirements of heavy robotic arms.

[0005] Electromagnetic direct-drive linear motor technology theoretically eliminates intermediate transmission links, directly generating linear thrust. Existing technologies primarily fall into two configurations: moving coil and moving magnet. The moving coil structure uses a coil assembly as the mover, which reduces moving mass, but is limited by coil heat dissipation, typically resulting in a sustained thrust density of no more than 50 N / cm². The moving magnet structure utilizes a permanent magnet array as the mover, which can increase thrust density to 80 N / cm². However, this requires a complex magnetic yoke structure, increasing the effective air gap length by over 30%. A more significant issue is that, to maintain sufficient electromagnetic coupling area, the radial dimensions of both structures often reach 1.5-2 times the effective stroke. For example, one model of a moving magnet linear motor with a 50 mm stroke has an outer diameter of 85 mm, severely limiting its integration into multi-degree-of-freedom joints. Furthermore, the end effects of existing linear motors can cause thrust fluctuations exceeding 15%, making them prone to creep during low-speed precision control.

[0006] In summary, existing linear motors, whether moving magnet or moving coil, have the problems of low load capacity and short working stroke. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to improve the load capacity and adaptively adjust the working stroke. In order to overcome the defects of the above-mentioned prior art (or related art), the present invention provides a linear actuator.

[0008] The present invention provides a linear actuator, comprising: A base assembly, wherein a first stator yoke is provided on the top of the base assembly; A second stator yoke is coaxially disposed on the top of the first stator yoke. The bottom of the second stator yoke is provided with a coaxial accommodating cavity and an annular cavity with an opening at the top. The inner diameter of the annular cavity is larger than the diameter of the accommodating cavity. A coaxial boss is provided on the top of the second stator yoke, and the opening at the top of the accommodating cavity penetrates the boss. A coaxial actuating magnet is fixed to the inner circumferential wall of the annular cavity. A capping assembly, wherein the bottom end of the capping assembly is provided with an annular air float, which is sleeved on the outer side of the second stator iron yoke and can move in the axial direction; The coil skeleton is fixed to the bottom end of the capping assembly and is located on the inner side of the air float. The bottom end of the coil skeleton is provided with a coaxial actuating coil and a compensating magnet in sequence from the outside to the inside in the radial direction. The actuating coil enters the annular cavity through the top opening of the annular cavity and can move in the axial direction. The compensating magnet enters the accommodating cavity through the top opening of the accommodating cavity and can move in the axial direction. The annular air-floating stator is arranged on the top of the first stator iron yoke and sleeved on the outer side of the air-floating stator. A plurality of vent holes for ventilation are opened on the outer wall of the air-floating stator.

[0009] Compared with the prior art, the linear actuator of this application has the following advantages: The present application adopts a voice coil motor driving method. In the initial state, the bottom end of the compensation magnet abuts against the top of the first stator iron yoke, the bottom end of the actuating coil abuts against the bottom of the annular cavity, and the bottom end of the air float abuts against the top of the first stator iron yoke. After power is turned on, the actuating coil and the actuating magnet generate electromagnetic force, driving the coil frame to perform linear motion. The actuating force is compensated by the attraction between the actuating magnet and the second stator iron yoke, and the compensation force and working stroke are adjusted by the stepped structure design between the boss and the inner wall of the annular cavity. In the process of the compensation magnet moving into the accommodating cavity, the volume of the actuating magnet part that provides attraction remains constant during the working stroke, which is the key to achieving stable compensation force. In this way, any working stroke can be achieved by adjusting the height of the boss and the annular cavity and the setting position of the actuating magnet. By cooperating with the air float and the air floating stator, the mechanical friction is reduced by gas lubrication introduced through the air vent, so that high-precision, low-loss linear motion can be achieved.

[0010] In one possible embodiment, a coaxial fixing ring is provided at the bottom end of the coil frame, the inner peripheral wall of the fixing ring abuts against the actuating magnet, and a coaxial and annular fixing plate is provided on the outer peripheral wall of the fixing ring, and the actuating coil is fixed to the top of the fixing plate.

[0011] Compared with the existing technology, the above technical solution can enhance the mechanical fixation of the actuating coil through the clamping structure formed by the fixing ring and the fixing plate, prevent the actuating coil from shifting or deforming due to high-frequency vibration, and the fixing ring is in direct contact with the actuating magnet, which can optimize the magnetic circuit closure path, reduce magnetic resistance, and improve energy conversion efficiency.

[0012] In a possible implementation, the actuating magnet includes a plurality of tile-shaped magnets, and each tile-shaped magnet is evenly distributed on the inner circumferential wall of the annular cavity along the circumferential direction.

[0013] Compared with the existing technology, the above technical solution forms a continuous and symmetrical annular magnetic field through the circumferential uniform distribution of tile-shaped magnets, reduces torque fluctuations, and ensures smooth movement.

[0014] In a possible implementation, the actuating magnets are magnetized radially, and the magnetization directions of adjacent tile-shaped magnets are opposite.

[0015] Compared with the existing technology, the above technical solution makes the magnetization directions of adjacent tile-shaped magnets opposite to each other, forming an alternating magnetic field gradient, significantly enhancing the magnetic field strength and improving the output force density.

[0016] In a possible implementation, the cross section of the compensating magnetic steel is circular, and is magnetized in a horizontal direction.

[0017] Compared with the existing technology, after adopting the above technical solution, the shape of the compensation magnet and the accommodating cavity are matched, which can optimize the magnetic flux distribution and accurately offset the leakage magnetic interference of the actuating coil.

[0018] Compared with the existing technology, the above technical solution adopts the layered design of three iron yoke segments to achieve segmented guidance of the magnetic circuit, reduce the risk of magnetic saturation, and improve the overall magnetic performance. At the same time, the stepped structure can achieve a compact layout, reduce the size of the device, and ensure the synergistic effect of the actuating magnet and the compensating magnet.

[0019] In a possible implementation manner, a fixing block is provided on the top end of the coil skeleton, and the compensating magnetic steel is fixed to the bottom end of the fixing block.

[0020] Compared with the prior art, the above technical solution prevents the compensating magnet from loosening during movement through the rigid connection between the fixed block and the compensating magnet, thereby ensuring the stability of the magnetic field.

[0021] In one possible embodiment, a reduced diameter portion is provided on the inner circumferential wall of the annular cavity and is located at the top of the annular cavity. The diameter of the reduced diameter portion is smaller than the diameter of the second stator yoke, and the actuating magnet is fixed on the outer circumferential wall of the reduced diameter portion.

[0022] Compared with the existing technology, the above technical solution adopts the layered design of the boss, the reduced diameter part and the inner wall of the annular cavity to realize segmented guidance of the magnetic circuit, reduce the risk of magnetic saturation, and improve the overall magnetic performance. At the same time, the stepped structure can achieve a compact layout, reduce the size of the device, and ensure the synergistic effect of the actuating magnet and the compensating magnet.

[0023] In a possible implementation, a nano-ceramic coating is provided on the outer peripheral wall of the air float, and the surface roughness of the nano-ceramic coating is no greater than 0.1 μm.

[0024] Compared with the existing technology, the above technical solution reduces the friction coefficient of the air float surface through nano-ceramic coating, prolongs the service life, and adapts to the needs of high-speed movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a cross-sectional schematic diagram of the present invention; Figure 3 A schematic diagram of the partial structure of the compensation magnetic steel of the present invention; Explanation of the accompanying drawings: 1. Base assembly; 2. First stator yoke; 3. Second stator yoke; 4. Accommodating cavity; 5. Annular cavity; 6. Boss; 7. Actuating magnet; 8. Capping assembly; 9. Air float; 10. Coil frame; 11. Actuating coil; 12. Compensating magnet; 13. Air float stator; 14. Vent; 15. Fixing ring; 16. Fixing plate; 17. Fixing block; 18. Reduced diameter portion. DETAILED DESCRIPTION

[0026] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of the present application and are not intended to limit the scope of protection of the embodiments of the present application. Those skilled in the art may adjust them as needed to suit specific application scenarios.

[0027] The present application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] See also Figure 1-Figure 3 The embodiment of the present application discloses a linear actuator, which uses the integrated design of a voice coil motor and a magnetic spring to solve the problems of low load capacity and short working stroke of the current direct-drive linear actuator, and uses magnetic levitation to improve the dynamic response speed and actuation efficiency. The present invention mainly includes three parts: an actuating component, a compensation component, and an air-floating sleeve. Among them, the air-floating sleeve includes an air float 9 with a hollow interior and an air-floating stator 13. A vent 14 is provided on the air float 9, and an internal air path is provided in the vent 14. The air float 9 is clamped on the inner side of the air-floating stator 13 and can move along the height direction of the air-floating stator 13; the actuating component is provided on the inner side of the air-floating stator 13, and includes a second stator yoke 3, an actuating magnet 7, an actuating coil 11 and a compensation magnet. 12 is a compensation component. The second stator yoke 3 is fixed on the first stator yoke 2 and a receiving chamber 4 is provided inside the second stator yoke 3. The cross section of the receiving chamber 4 is circular. An annular chamber 5 is provided between the receiving chamber 4 and the outer peripheral wall of the second stator yoke 3. The top of the second stator yoke 3 is provided with a circular through hole communicating with the receiving chamber 4 and a circular through hole identical to the annular chamber 5. An actuating magnet 7 is fixed on the inner peripheral wall of the circular through hole. The bottom end of the entire device is a base component 1, and the top end is a capping component 10. The top of the base component 1 is provided with a first stator yoke 2, and the bottom end of the capping component 8 is provided with an air float 9. The air float 9 is sleeved on the outside of the second stator yoke 3 and can move axially. All of the above components are coaxially arranged.

[0029] In the embodiment of the present application, the coil skeleton 10 is fixed to the bottom end of the capping assembly 8 and is located on the inner side of the air float 9. The bottom end of the coil skeleton 10 is provided with an actuating coil 11 and a compensating magnet 12 in sequence along the radial direction from the outside to the inside. The actuating coil 11 is located in the annular cavity 5 and is movable, and the compensating magnet 12 is located in the accommodating cavity 4 and is movable.

[0030] In the embodiment of the present application, the air-floating stator 13 is provided at the top of the first stator yoke 2 and sleeved on the outside of the air float 9 . A plurality of vent holes 14 are provided on the outer wall of the air-floating stator 13 for arranging an air path.

[0031] In the embodiment of the present application, the internal air path of the vent 14 can adopt a multi-stage throttling hole design, the diameter of the throttling hole decreases gradually along the air flow direction, and the spacing between adjacent throttling holes is positively correlated with the stroke of the air float 9. The throttling hole diameter range is determined to be 0.2-0.8mm through CFD simulation. When the spacing is 1 / 5-1 / 3 of the stroke, a stable air film with a thickness of 0.01-0.05mm can be formed, and the friction resistance can be greatly reduced.

[0032] In the embodiment of the present application, the outermost portion of the linear actuator is an air-floating sleeve, the middle portion is an actuating assembly, an air path is arranged in the middle of the air-floating sleeve, and an air film exists when the middle of the air-floating sleeve is ventilated.

[0033] In the embodiment of the present application, a fixing ring 15 is provided at the bottom end of the coil skeleton 10, the inner peripheral wall of the fixing ring 15 is in contact with the actuating magnet 7, and a fixing plate 16 is provided on the outer peripheral wall of the fixing ring 15, and the actuating coil 11 is fixed between the fixing plate 16 and the coil skeleton 10.

[0034] In the embodiment of the present application, the actuating magnet 7 includes a plurality of tile-shaped magnets, and each tile-shaped magnet is evenly distributed on the inner circumferential wall of the annular cavity 5 along the circumferential direction.

[0035] In the embodiment of the present application, the actuating magnet 7 is made of neodymium iron boron N52UH brand, with an axial magnetization direction and a single tile-shaped magnet with an arc of 60°. The compensating magnet 12 is an annular samarium cobalt magnet, which is radially magnetized. Its inner diameter is matched with the gap of the second stator iron yoke 3 accommodating cavity 4, and the gap value is controlled at 0.1-0.3mm to optimize the leakage magnetic rate.

[0036] In the embodiment of the present application, a reduced diameter portion 18 is provided on the inner circumferential wall of the annular cavity 5 and the reduced diameter portion 18 is located at the top of the annular cavity 5 . The diameter of the reduced diameter portion 18 is smaller than the diameter of the second stator yoke 3 , and the actuating magnet 7 is fixed on the outer circumferential wall of the reduced diameter portion 18 .

[0037] In the embodiment of the present application, a fixing block 17 is provided at the top end of the coil bobbin 10 , and the compensation magnetic steel 12 is fixed to the bottom end of the fixing block 17 .

[0038] In the embodiment of the present application, the linear actuator uses a voice coil motor drive method, and uses the attraction between the second stator yoke 3 and the actuating magnet 7 to compensate for the actuating force. Assuming that the permanent magnet is uniformly magnetized, there is an attraction between the magnet and the ferromagnetic material. During the movement of the compensation magnet 12 into the accommodating cavity 4 in the second stator yoke 3, the volume of the actuating magnet 7 that provides the attraction remains constant during the working stroke. This is the key to achieving a stable compensation force. In this way, any working stroke can be achieved by adjusting the height of the boss 6 and the height of the actuating magnet 7. However, in actual movement, due to the existence of the air gap, the magnetic resistance is constantly increasing, so it is necessary to increase the attraction to compensate for the loss of attraction due to the increase in magnetic resistance. Changing the inner diameter of the second stator yoke 3 can achieve this. The adjustment of the air gap will significantly increase the attraction, which ensures the constancy of the compensation force and also achieves the adjustment of the compensation force value.

[0039] In the embodiment of the present application, the current mainstream linear actuator does not use a direct drive motor such as a voice coil motor. The reason is that the voice coil motor has a weak load capacity and a serious temperature rise under high load. In order to solve this problem, the present invention uses the electromagnetic force generated between the actuating magnet 7 and the second stator iron yoke 3 to compensate for the force required by the voice coil motor, which greatly improves the load capacity of the voice coil motor as a linear actuator and reduces power consumption. It also gives full play to the advantages of the voice coil motor's small size and good linearity between thrust and current. Furthermore, using the electromagnetic force between the actuating magnet 7 and the second stator iron yoke 3 to compensate for the voice coil motor will result in There are some problems. The first is that electromagnetic force is often nonlinear. If it is not corrected, it will affect the linear force output by the voice coil motor. The present invention uses a horizontally magnetized cylindrical compensation magnet 12 and a second stator iron yoke 3 with a stepped inner diameter to achieve an electromagnetic force with good linearity. At the same time, the working stroke and size of the constant force section of the electromagnetic force can be adjusted, and the magnetic levitation motor design also avoids mechanical wear and greatly improves the service life. By applying this method, there must be an optimal iron yoke inner diameter curve under a certain size, which can achieve constant compensation force. Using an air-floating bushing as a linear motion guide, the motion resistance is small, the friction is zero, and the service life is long.

[0040] In an embodiment of the present application, the linear actuator may further include a position sensor assembly, which includes a Hall sensor array arranged at the end of the air-floating stator 13 and a magnetic encoder arranged on the compensation magnet 12. The outer surface of the air-floating stator 9 is provided with a nano-ceramic coating, and its surface roughness is not greater than 0.1 μm.

[0041] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0042] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A linear actuator, characterized in that: include: A base assembly (1), wherein a first stator yoke (2) is provided at the top end of the base assembly (1); A second stator iron yoke (3) is coaxially arranged at the top of the first stator iron yoke (2); a coaxial accommodating cavity (4) and an annular cavity (5) are provided at the bottom of the second stator iron yoke (3); the inner diameter of the annular cavity (5) is larger than the diameter of the accommodating cavity (4); a coaxial boss (6) is provided at the top of the second stator iron yoke (3); and the top opening of the accommodating cavity (4) passes through the boss (6); and a coaxial actuating magnet (7) is fixed on the inner peripheral wall of the annular cavity (5); A capping assembly (8), wherein the bottom end of the capping assembly (8) is provided with an annular air float (9), and the air float (9) is sleeved on the outer side of the second stator iron yoke (3) and can move in the axial direction; The coil frame (10) is fixed to the bottom end of the capping assembly (8) and is located on the inner side of the air float (9). The bottom end of the coil frame (10) is provided with a coaxial actuating coil (11) and a compensating magnetic steel (12) in sequence along the radial direction from the outside to the inside. The actuating coil (11) enters the annular cavity (5) along the top opening of the annular cavity (5) and can move in the axial direction. The compensating magnetic steel (12) enters the accommodating cavity (4) along the top opening of the accommodating cavity (4) and can move in the axial direction. The annular air-floating stator (13) is arranged at the top end of the first stator iron yoke (2) and is sleeved on the outside of the air-floating stator (9). A plurality of vent holes (14) for ventilation are provided on the outer wall of the air-floating stator (13).

2. The linear actuator according to claim 1, characterized in that A coaxial fixing ring (15) is provided at the bottom end of the coil frame (10), the inner peripheral wall of the fixing ring (15) is in contact with the actuating magnet (7), and a coaxial and annular fixing plate (16) is provided on the outer peripheral wall of the fixing ring (15), and the actuating coil (11) is fixed to the top end of the fixing plate (16).

3. The linear actuator according to claim 1, wherein The actuating magnetic steel (7) comprises a plurality of tile-shaped magnets, each tile-shaped magnet being uniformly distributed along the circumferential direction on the inner peripheral wall of the annular cavity (5).

4. The linear actuator according to claim 3, characterized in that The actuating magnetic steel (7) adopts a radial magnetization method and the magnetization directions of adjacent tile-shaped magnets are opposite.

5. The linear actuator according to claim 1, wherein The cross section of the compensation magnetic steel (12) is circular and is magnetized in a horizontal direction.

6. The linear actuator according to claim 1, wherein A fixing block (17) is provided at the top end of the coil frame (10), and the compensation magnetic steel (12) is fixed to the bottom end of the fixing block (17).

7. The linear actuator according to claim 1, wherein A reduced diameter portion (18) is provided on the inner peripheral wall of the annular cavity (5), and the reduced diameter portion (18) is located at the top of the annular cavity (5). The diameter of the reduced diameter portion (18) is smaller than the diameter of the second stator iron yoke (3), and the actuating magnet (7) is fixed on the outer peripheral wall of the reduced diameter portion (18).

8. The linear actuator according to claim 1, wherein A nano-ceramic coating is provided on the outer peripheral wall of the air float (9), and the surface roughness of the nano-ceramic coating is not greater than 0.1 μm.

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