Large-reduction-ratio robot joint actuator with built-in speed reduction structure

Abstract

The utility model discloses a large reduction ratio robot joint actuator with a built-in speed reduction structure, which comprises two inner gear rings, a plurality of planet gears, an actuator shell and an actuator cover plate, an accommodating space is formed between the actuator shell and the actuator cover plate, a motor stator and a motor rotor are arranged in the accommodating space, and the motor stator is connected with the motor rotor. The motor stator is fixed to the actuator shell. A plurality of planet gears are arranged in the two inner gear rings, the planet gears are evenly distributed in the circumferential direction of the inner gear rings, each planet gear is meshed with the two inner gear rings, and the meshing center distances are kept equal; the two inner gear rings are the same in modulus and unequal in tooth number, and the two inner gear rings are the fixed gear ring and the output gear ring respectively. The whole axial size of the actuator is compact, under the condition that a speed reduction structure is extremely simple, the larger speed reduction ratio, the larger gear modulus and the larger gear width are obtained compared with a conventional speed reduction scheme, the strength and the bearing capacity of the actuator are greatly improved, the service life of the actuator is greatly prolonged, the assembly technology is simple, cost is low, and the structure is reliable.

Description

Technical Field

[0001] The utility model belongs to the technical field of robots, and particularly relates to a joint part in a robot body structure. Background Art

[0002] In the field of robot applications, the number of degrees of freedom, motion ability, and precise control of various complex postures of its products are all determined and completed by actuators in different parts of the robot body structure. An actuator is a basic motion and control unit composed of a motor, a reducer, a motor drive controller, and other optional accessories. When the robot is working, in addition to bearing specific working loads (such as heavy objects grasped by a manipulator, working loads carried by a legged robot, etc.), it also needs to overcome its own structural weight, and high torque needs to be burst out by the actuator when the posture and motion are complex. For bipedal humanoid robots, quadruped and multi-legged robots powered by lithium batteries themselves, due to the large weight of the lithium batteries, the robot body structure is highly complex and integrated with various sensors, electronic modules, and computing and control units, and there are high requirements for the shape and volume of the robot. Therefore, the integration degree, complexity, and technical difficulty of the system are much higher than those of conventional industrial robots. Therefore, bipedal humanoid robots are often regarded as the crown in modern manufacturing. The joint actuator is the most critical core component in the robot body structure, and its performance directly determines the basic motion ability, flexibility, and posture control ability of the robot.

[0003] The prior art is to cooperate a brushless motor with a reducer, so that the motor works in a high-speed and high-efficiency area, and relies on the reduction of the reducer to provide an amplified output torque. Existing actuator products generally adopt one or more of the following technologies:

[0004] The motor and the reducer are designed and manufactured separately, and finally the two components are assembled in series axially. Such a scheme will lead to too large an axial dimension of the entire actuator, increased weight, too many parts, which will bring about an increase in process cost and a reduction in reliability. Since the strength and load-bearing capacity of a gear are jointly determined by the module and width of the gear, it is generally difficult to adjust the gear module due to the limitation of the radial dimension space. In order to avoid too large an axial dimension, the gear width must be reduced, resulting in insufficient gear load-bearing capacity and shortening the service life of the reducer gear;

[0005] Figures 3 - 4It is a common design solution for a robot joint actuator. From this design solution diagram, it can be known that the sun gear of the planetary reducer is press-fitted onto the motor rotor by interference fit. The motor and the reducer are in an axial series structure. In order to prevent the axial length of the entire actuator from being too long, the tooth widths of all gears in the reducer (sun gear, planetary gear, internal gear ring) are designed to be very small (generally 3-5 mm). Therefore, the gear strength is low, and the load-bearing capacity and service life are very limited.

[0006] To increase the output torque of the actuator, the most commonly thought-of method is to increase the reduction ratio of the reducer to improve the amplification ability of the motor torque. There are two conventional methods. One is to increase the number of teeth of the internal gear (which will also cause a decrease in the gear modulus and a reduction in gear strength) and appropriately reduce the number of teeth of the sun gear (too few teeth will cause gear undercutting and also reduce gear strength) to increase the reduction ratio. The other method is to increase the reduction ratio by axially connecting two or more planetary reducers in series. Multiple series connections will also face a reduction in the actual gear width of each stage of transmission, too many gears, and the gears and planet carriers cannot be effectively supported by bearings, which will overall bring many adverse effects such as complex processes, difficult assembly, reduced rotational accuracy and stiffness, high cost, and low reliability.

[0007] Figure 1 and Figure 2Shows a common two - stage planetary axial series scheme in a robotic joint actuator. In this scheme, the output torque of the motor is input into the first - stage planetary reducer through the first - stage sun gear press - fitted on the motor rotor. The first - stage planetary reducer consists of the first - stage sun gear, the first - stage planet gears, the first - stage internal gear ring (rigidly fixed to the actuator housing), and the first - stage planet carrier. Note that the first - stage planet gears are supported on a very thin sheet - type (first - stage) planet carrier through their planet pin columns on one side only. The first - stage planet carrier is in a "floating state" and cannot be supported by reliable and effective means such as bearings. The support effect of the first - stage planet carrier on the first - stage planet gears is very poor. One end of its planet pin column is supported on the planet carrier, and the other end is suspended, in a "cantilever beam" state, with very poor stiffness. The output torque of the first - stage reducer is output by the first - stage planet carrier and is input into the second - stage planetary reducer through the second - stage sun gear rigidly connected to it. The second - stage planetary reducer consists of the second - stage sun gear, the second - stage planet gears, the second - stage internal gear ring (rigidly fixed to the actuator housing), and the second - stage planet carrier (output flange). Its principle, structure, and drawbacks are similar to those of the first - stage, that is: the second - stage planet carrier (output flange) also supports the second - stage planet gears in a "cantilever beam" manner, and the second - stage planet gears cannot be supported reliably and effectively. In this two - stage planetary reduction structure, neither axially nor radially can effective and reliable support be obtained. The whole structure has numerous components, and both the structure and assembly are very complex. The overall structural reliability and precision are relatively low (according to the theory of precision and reliability, the more components there are, the greater the risk factors of failure, the greater the complexity of the system, and the total reliability and total precision will also decrease sharply). Because there are many components, various error accumulations will also increase the overall noise of the actuator. Since the torque of the first - stage reducer is small and the torque of the second - stage reducer is large, in this scheme, a distribution scheme of a smaller module and smaller tooth width for the first - stage and a larger module and larger tooth width for the second - stage (output stage) is often adopted, which will result in the need to prepare gear hobs of different modules, increasing the specifications, types, and costs of gear - cutting tools, leading to disadvantages such as poor economy and increased management costs. It can be clearly seen from the structure diagram that the tooth width of each stage of the gear is still very small, generally about 4 mm, and the load - bearing capacity of the gear is extremely limited.

[0008] Figure 5Shows another common "dual planetary" deceleration scheme in a robotic joint actuator, that is, replacing the single "planetary gear" in a conventional planetary reducer with a gear set composed of two axially rigidly connected gears of different sizes, one large and one small. This gear set of one large and one small is often called a "dual planetary gear". In a dual planetary gear, there is a natural reduction ratio between the two gears of different sizes. The output power of the motor is first transmitted from the sun gear to the large gear in the dual planetary gear through its meshing motion, then undergoes the inherent deceleration of the dual planetary gear, and is then output by the small gear in the dual planetary gear and meshes with the internal gear ring. The dual planetary gear, as a whole, participates in the transmission of the entire reducer together with the planet carrier. Therefore, the reduction ratio of the dual planetary gear is slightly larger than that of a conventional single-stage planetary reducer. The common reduction ratio range is 10 - 18 (it will be very difficult to increase further). It can be clearly seen from the schematic diagram that the total axial width of the reducer in the dual planetary scheme will become larger (the axial width of an externally protruding large dual planetary gear is increased), and the overall outer diameter of the large dual planetary gear will be larger than the outer diameter of the internal gear ring. Therefore, the overall radial size of the reducer will also increase. At the same time, there are strict requirements for the relative radial positions between the teeth of the large and small gears in the dual planetary gear, and "tooth alignment" operations are required, which is troublesome in terms of technology and will increase costs.

[0009] Another common deceleration scheme is to use a harmonic reducer (see Figure 6 ). The principle of a harmonic reducer is that the output power of the motor is connected to the wave generator, the rigid gear is fixed to the housing, and the flexible gear outputs power (the flexible gear is fixed to the output flange with screws); the ultra-thin flexible bearing on the wave generator and the wall thickness of the flexible gear must be made very thin so that they can undergo the required specific elastic deformation synchronously with the rotation of the wave generator, pushing the teeth on the flexible gear and the teeth on the rigid gear to continuously perform slow misaligned tooth rotation movements; the advantage of a harmonic reducer is that the reduction ratio is slightly larger (commonly between 40 - 150), but this is only in comparison with conventional deceleration schemes (except for the technology of this patent), and harmonic drive also has its technical weaknesses: the wall thicknesses of its flexible gear and flexible bearing are very thin, the material rigidity is poor, there are elastic angular deformations and lags at the output and input ends, and because the material is in continuous elastic deformation, its fatigue strength is far lower than that of common gear materials, the flexible gear and flexible bearing are easily damaged, the load-bearing capacity and service life are both limited, the raw materials need to be imported, the price is expensive (the price is several times to dozens of times that of a planetary reducer), and the transmission efficiency is not dominant (generally about 75%, and the efficiency is still relatively low), etc.;

[0010] In summary, the existing robotic joint actuators have the following many deficiencies: it is very difficult to increase the reduction ratio, the gear strength and load-bearing capacity are generally low (the module is small and the gear tooth width is small), the structure of a conventional reducer is too complex, the assembly is difficult, the reliability is low, the overall size is too large, there are too many components, the weight is too heavy, and the cost remains high. Summary of the Utility Model

[0011] The main technical problem to be solved by the present utility model is to provide a large reduction ratio robot joint actuator with an internal reduction structure, which has an extremely compact overall axial dimension. Under the condition of extremely simplified reduction structure, a larger reduction ratio, larger gear module and width are obtained, and its strength, bearing capacity and service life are greatly improved. The assembly process is simple, the cost is low, and the structure is reliable.

[0012] To solve the above technical problem, a technical solution adopted by the present utility model is: a large reduction ratio robot joint actuator with an internal reduction structure, which includes two internal gear rings, several planet gears, an actuator housing and an actuator cover plate. A containing space is jointly formed between the actuator housing and the actuator cover plate, and a motor stator and a motor rotor are installed inside the containing space. The motor stator is fixed to the actuator housing;

[0013] Several planet gears are arranged inside the two internal gear rings, and the several planet gears are evenly arranged along the circumferential direction of the internal gear rings. Each planet gear meshes with the two internal gear rings and the meshing center distance remains equal;

[0014] The two internal gear rings are internal gear rings with the same module and different numbers of teeth. The two internal gear rings are respectively a fixed gear ring and an output gear ring. The fixed gear ring is installed on the actuator housing, and the output gear ring is installed on the output flange. The planet gears revolve around the central axis of the two internal gear rings under the direct or indirect drive of the motor rotor, and the planet gears can rotate around their own central axes. The two internal gear rings and the several planet gears constitute a single-stage reduction structure, which has an extremely compact overall axial dimension. Under the condition of extremely simplified reduction structure, a larger reduction ratio, larger gear module and width are obtained, and its strength, bearing capacity and service life are greatly improved.

[0015] Further, the difference in the number of teeth between the fixed gear ring and the output gear ring is equal to the number of planet gears.

[0016] Further, the several planet gears are rotatably connected to a planet carrier, and the planet carrier is fixed to the motor rotor.

[0017] Further, the teeth on the surface of the planet gear are herringbone teeth, and the herringbone teeth are composed of two symmetrically arranged helical teeth.

[0018] Further, a hollow shaft is installed at the center of the actuator. The hollow shaft is fixed to the output flange, which can realize "hollow wire routing" in robot wiring, reduce the wiring difficulty, avoid the exposure of cables, and avoid the damage of wire materials while being beautiful.

[0019] Furthermore, a sun gear is installed at the center of the actuator, and the sun gear is fixed to the motor rotor. A number of planet gears are located between the sun gear and the two internal gear rings, and the planet gears are respectively meshed with the sun gear.

[0020] Furthermore, a central through hole is provided at the center of the sun gear, which can achieve "hollow wire routing" in robot wiring, reduce the wiring difficulty, avoid cable exposure, and avoid wire damage while being aesthetically pleasing.

[0021] Furthermore, a grease storage groove is provided on the inner peripheral surface of the output flange or the actuator housing, or grease storage holes are arranged in a ring.

[0022] Furthermore, the output flange is provided with pin columns and threaded holes for external connection and power transmission.

[0023] The beneficial effects of the present utility model at least include the following points:

[0024] The two internal gear rings and a number of planet gears of the present utility model form a single-stage reduction structure. A number of planet gears are provided inside the two internal gear rings, and the planet gears are evenly arranged along the circumferential direction of the internal gear rings. Each planet gear is meshed with the two internal gear rings and the meshing center distance remains equal. The overall axial dimension is extremely compact. In the case of an extremely simple reduction structure, a reduction ratio larger than that of a conventional reduction scheme is obtained, as well as a larger gear module and width. Its strength, load-bearing capacity, and service life are greatly improved. The assembly process is simple, the cost is low, and the structure is reliable.

[0025] A hollow shaft or a central through hole is provided at the center of the actuator of the present utility model, which can achieve "hollow wire routing" in robot wiring, reduce the wiring difficulty, avoid cable exposure, and avoid wire damage while being aesthetically pleasing.

[0026] The present utility model realizes a large gear module, large tooth width, and large transmission ratio. The gear module in the conventional robot joint actuator is increased by 2.5 times, the tooth width is increased by 3 times, the load-bearing capacity and service life are increased by more than 7 - 10 times, and the reduction ratio can achieve a wide range of 14 - 400. Compared with the multi-stage planetary series scheme and the harmonic reducer, it has significant advantages.

[0027] In this utility model, the sun gear is fixedly press-fitted onto the motor rotor. The motion and power of the motor are input into the sun gear by the motor rotor, thus eliminating the planet carrier, which can significantly reduce the cost of the reduction structure and has remarkable cost-effectiveness. In a planetary reducer, the cost of the planet carrier accounts for at least more than one-third of the total cost. The overall structure of the planet carrier is complex, and several pin holes for the planet gears of the planet carrier need to be processed by high-precision processing equipment to ensure the high precision of planetary rotation. Therefore, omitting this part and canceling the relatively complex, cumbersome, time-consuming and labor-intensive planet gear press-fitting during assembly (the labor cost accounts for a large proportion) can significantly reduce the assembly and process costs, enabling the total cost of the reduction structure to be reduced by more than 70%. It is worth mentioning that due to the floating of several planet gears evenly distributed in the circumference, when the planet gears are under the combined torque and force of the internal gear ring and the sun gear, the relative positions of the planet gears can be adjusted adaptively to ensure that the planet gears evenly distributed in the circumference can jointly share the torque and force evenly, realizing the automatic average distribution of the load between the planet gears and extending the service life of the reduction structure;

[0028] The reduction ratio of this utility model is larger than that of the harmonic reducer. Secondly, due to the natural disadvantages in its principle and materials, the strength and durability of the harmonic reducer (the fatigue life of the material is much lower than the meshing life of the gear material) are far lower than those of the large module and large reduction ratio planetary gear transmission of this patent. In terms of transmission efficiency, the efficiency of the harmonic reducer is about 75%, while the transmission efficiency of this patented technology is about 90%. Finally, the cost of the harmonic reducer is several times to dozens of times that of the planetary reducer, which constitutes a great obstacle to the cost reduction and commercial mass production of humanoid robots. Description of the Drawings

[0029] Figure 1 is a cross-sectional view of a two-stage planetary transmission actuator of the prior art;

[0030] Figure 2 is an exploded view of a two-stage planetary transmission actuator of the prior art;

[0031] Figure 3 is a cross-sectional view of a series-structure actuator of the prior art;

[0032] Figure 4 is an exploded view of a series-structure actuator of the prior art;

[0033] Figure 5 is an exploded view of a double planetary gear reducer actuator of the prior art;

[0034] Figure 6 is a cross-sectional view of a harmonic reducer of the prior art;

[0035] Figure 7 is a cross-sectional view of the first embodiment of this utility model;

[0036] Figure 8 is an exploded schematic view of the first embodiment of the present utility model;

[0037] Figure 9 is a structural schematic view of the planet carrier and planet gears of the first embodiment of the present utility model;

[0038] Figure 10 is a cross-sectional view of the second embodiment of the present utility model;

[0039] Figure 11 is an exploded schematic view of the second embodiment of the present utility model;

[0040] Figure 12 is a structural schematic view of the output flange of the present utility model;

[0041] The reference signs of each part in the drawings are as follows:

[0042] 1. Planet gear; 11. Herringbone tooth; 21. Actuator housing; 22. Actuator cover plate; 31. Motor stator; 32. Motor rotor; 4. Fixed ring gear; 5. Output ring gear; 6. Output flange; 61. Output flange support bearing; 7. Planet carrier; 71. Planet carrier support bearing; 8. Hollow shaft; 81. Hollow shaft support bearing; 9. Sun gear; 91. Central through hole; 92. Sun gear support bearing; 10. Grease storage hole. Detailed implementation manners

[0043] The following elaborates on the preferred embodiments of the present utility model in conjunction with the drawings, so that the advantages and features of the present utility model can be more easily understood by those skilled in the art, thereby making the protection scope of the present utility model more clearly defined.

[0044] Embodiment 1: A large reduction ratio robot joint actuator with an internal reduction structure, as Figures 7 - 8 shown, includes two internal ring gears, several planet gears 1, an actuator housing 21 and an actuator cover plate 22. A accommodation space is jointly formed between the actuator housing 21 and the actuator cover plate 22. A motor stator 31 and a motor rotor 32 are installed inside the accommodation space, and the motor stator 31 is fixed to the actuator housing 21;

[0045] In this embodiment, an outer rotor brushless motor is installed inside the accommodation space, and the outer rotor brushless motor includes a motor stator and a motor rotor;

[0046] Several planet gears 1 are provided inside the two internal ring gears, and several planet gears 1 are evenly arranged along the circumferential direction of the internal ring gear. Each planet gear 1 meshes with the two internal ring gears and the meshing center distance remains equal;

[0047] The two internal gear rings are internal gear rings with the same module but different numbers of teeth. The two internal gear rings are respectively a fixed gear ring 4 and an output gear ring 5. The fixed gear ring 4 is installed on the actuator housing 21, and the output gear ring is installed on the output flange 6. The planet gear 1 revolves around the central axis of the two internal gear rings under the direct or indirect drive of the motor rotor 32, and the planet gear 1 can rotate around its own central axis, achieving large module, large tooth width and large transmission ratio of the gear. Compared with the gears in conventional robot joint actuators, the gear module is increased by 2.5 times, the tooth width is increased by 3 times, the load-bearing capacity and service life are increased by more than 7-10 times, and the reduction ratio can achieve a wide range of 14-400. Compared with the multi-stage planetary series scheme and the harmonic reducer, it has significant advantages;

[0048] During specific implementation, a motor drive controller (not shown in the figure) is installed on the actuator cover plate.

[0049] The difference in the number of teeth between the fixed gear ring 4 and the output gear ring 5 is equal to the number of planet gears 1. The number of planet gears 1 is generally 2-4. When the planet gear revolves one week, due to the specific difference in the number of teeth between the two internal gear rings, the output gear ring will only advance or retreat by the same number of tooth pitches as this difference in the number of teeth relative to the fixed gear ring. Therefore, the revolution of the output gear ring relative to the planet gear forms a reduction ratio. Reduction ratio = number of teeth of the output gear ring / (number of teeth of the output gear ring - number of teeth of the fixed gear ring). When the number of teeth of the output gear ring > the number of teeth of the fixed gear ring, the rotation direction of the output gear ring is the same as the revolution direction of the planet gear, and vice versa.

[0050] A plurality of the planet gears 1 are rotatably connected to the planet carrier 7, and the planet carrier 7 is fixed to the motor rotor 32.

[0051] As Figure 9 shown, the teeth on the surface of the planet gear 1 are herringbone teeth 11, and the herringbone teeth 11 are composed of two symmetrically arranged helical teeth. Of course, in this embodiment, the gear of the planet gear can also be a helical tooth or a straight tooth, but it is not limited thereto. As long as it is other tooth structures that can make the planet gear mesh with the internal gear ring, they are all acceptable.

[0052] A hollow shaft 8 is installed at the center of the actuator, and the hollow shaft 8 is fixed to the output flange 6. In this embodiment, the hollow shaft is provided so that the robot cable can pass through this sufficiently large hollow aperture. If the wire threading is not considered, it can also be directly set as a solid shaft.

[0053] A planet carrier support bearing 71 is provided between the planet carrier and the actuator housing, an output flange support bearing 61 is provided between the output flange and the actuator housing, and a hollow shaft support bearing 81 is provided between the hollow shaft and the planet carrier.

[0054] In this embodiment, the following can be adopted Figures 7 - 9 Embodiment, that is, the rotor of the motor is directly locked on the planet carrier. The rotation of the motor rotor and the revolution of the planet gears are kept equal and synchronous, that is, the sun gear in the conventional actuator is cancelled, which can bring the following remarkable benefits:

[0055] 1. The sun gear is cancelled and the number of components is simplified, which can significantly reduce the cost of components and greatly improve the reliability, having significant advantages compared with common schemes such as two-stage planetary series connection and double planetary transmission;

[0056] 2. In the conventional planetary reduction scheme, the sun gear needs to be press-fitted onto the motor rotor with high precision to ensure coaxiality. Since the sun gear is cancelled, both the process difficulty and cost are reduced;

[0057] 3. Since the sun gear is cancelled, the space originally occupied by the sun gear is saved, forming a large middle hole space through which the robot cable can pass to achieve hollow wiring. In contrast, in the design of the existing conventional robot actuator, it is extremely difficult to open a hole in the middle and it is very difficult to achieve hollow wiring. Therefore, in currently common humanoid robots, the cables of the actuator are generally exposed outside, which not only affects the aesthetics but also easily catches the external exposed cables during the movement of the robot, posing a certain risk;

[0058] 4. In this scheme, the module of the gear is 1.25 module and the width of the internal gear ring reaches 14 mm. Compared with the robot joint actuators of the same size and reduction ratio on the market, the module is generally only about 0.5 module and the tooth width is mostly 4 - 5 mm. Since the strength and load-bearing capacity of the gear are jointly determined by the gear module and tooth width, the load-bearing capacity and service life of the reduction structure in this scheme can be increased by at least 7 - 10 times or more;

[0059] 5. In this embodiment, since the planet carrier only receives the output torque of the motor (relatively small) and does not bear the output torque after reduction (relatively large), the planet carrier can be made of lightweight alloy (such as aluminum alloy, etc.). Compared with the steel planet carrier in a general reducer, its weight can be reduced to 1 / 3 of the original, which is extremely beneficial for the lightweight of the robot;

[0060] 6. Helical gear transmission has the following advantages compared to spur gear transmission: large meshing overlap ratio, low noise, smooth transmission, and smaller gear backlash, thus having significant advantages. However, its disadvantage is the existence of axial force. In this embodiment, the planetary gears can adopt a herringbone tooth scheme, and the corresponding two internal gear rings respectively adopt helical gears with opposite helix directions; since the two sides of the herringbone tooth are helical gears with opposite helix directions, the axial forces on both sides can be offset. When the robot joint actuator rotates forward and backward frequently, while retaining many advantages of helical gear meshing, it also overcomes the drawback of axial force existing in conventional helical gears, having significant technical advantages.

[0061] 7. In this embodiment, an integral planetary carrier is adopted, that is, the planetary carrier is a complete whole. The pin holes of the planetary gears in the planetary carrier are machined in one go using a high-precision machine tool. The accuracy, consistency, rigidity, etc. of the pin holes on both sides of the planetary gears can all reach very high precision and guarantee, and higher transmission precision can be obtained. The backlash of its reduction structure can be made to 1 - 3 arc minutes. For conventional robot joint actuators, the planetary carriers of their reducers mostly adopt a split type (that is, the planetary carrier is divided into planetary carrier A and planetary carrier B, and then axially combined through screws, etc.), which has drawbacks such as low machining accuracy, large error, and poor rigidity. The backlash of its reducer is generally about 15 arc minutes. Therefore, it can overcome many drawbacks of the split-type planetary carrier, and thus can achieve high rigidity, high precision, very small backlash, and very low noise, reaching the transmission quality of the precision level;

[0062] The working principle of Embodiment 1 is as follows: The motor rotor drives the planetary carrier to rotate. The planetary carrier drives several planetary gears to revolve. Since the fixed gear ring meshes with the planetary gears, the planetary gears rotate on their own axes, and the planetary gears drive the output gear ring to rotate. The output gear ring drives the output flange to rotate.

[0063] Embodiment 2. The structure of this embodiment is basically similar to that of Embodiment 1. The difference is that, as Figures 10 - 11 shown, a sun gear 9 is installed at the center of the actuator of this embodiment. The sun gear 9 is fixed to the motor rotor 32. Several planetary gears 1 are located between the sun gear 9 and the two internal gear rings, and several planetary gears 1 respectively mesh with the sun gear 9.

[0064] A central through hole 91 is provided at the center of the sun gear 9.

[0065] An output flange support bearing is provided between the output flange and the actuator housing, and a sun gear support bearing 92 is provided between the sun gear and the output flange.

[0066] When a very high reduction ratio is required, it can be taken Figures 10 - 11Embodiment: That is, the sun gear is retained and fixedly press-fitted onto the motor rotor. The motion and power of the motor will be input from the motor rotor into the sun gear, and the sun gear will drive the circumferentially distributed planet gears to perform planetary motion of both self-rotation and revolution. The output after deceleration is the revolution motion of the planet gears (the revolution of the planet gears is synchronous with the planet carrier, and the planet carrier is removed in this embodiment). This is the principle of the first-stage deceleration (the same as the principle of a conventional planetary reducer). Due to the existence of the output ring gear, it has been briefly described before that the revolution of the planet gears (the output of the first-stage deceleration) and the two internal ring gears also form the principle of the second-stage deceleration. Therefore, the total reduction ratio is the first-stage reduction ratio × the second-stage reduction ratio, and thus a higher reduction ratio can be obtained;

[0067] In this embodiment, neither the revolution nor the self-rotation of the planet gears is affected by an external torque. By analyzing the forces on a single planet gear, it can be known that the planet gear is only subjected to three torques: the first is the torque transmitted by the sun gear to the planet gear (the torque load is evenly distributed within the entire gear width of the planet gear), the second is the reaction torque from the fixed ring gear on one side of the planet gear (the torque load is evenly distributed within the tooth width range of one side of the planet gear), and the third is the reaction torque from the output ring gear on the other side of the planet gear (the torque load is evenly distributed within the tooth width range of one side of the planet gear). The resultant torque of the combined action of the three torques on the planet gear is zero. Therefore, the "planet carrier" used to fix and support the planet gears and their revolution in a conventional planetary reducer can be eliminated in this embodiment, and the axial space of the planet carrier is defined by the housing seat on the left and the output flange on the right.

[0068] This embodiment can achieve the following remarkable benefits:

[0069] 1. Since the planet carrier is omitted, the cost of the deceleration structure can be significantly reduced, with significant cost-effectiveness. In a planetary reducer, the cost of the planet carrier accounts for at least more than one-third of the total cost. The overall structure of the planet carrier is complex, and the several planet pin holes of the planet carrier require high-precision processing equipment to ensure high-precision planetary rotation. Therefore, omitting this part and canceling the relatively complex, cumbersome, time-consuming, and labor-intensive planet gear press-fitting during assembly (the labor cost accounts for a large proportion) can significantly reduce the assembly and process costs, enabling the total cost of the deceleration structure to be reduced by more than 70%.

[0070] 2. In this embodiment, the sun gear still maintains a relatively large hollow through-hole, which can achieve hollow wire routing to reduce the wiring difficulty of the robot and avoid risks such as cable exposure, damage, and scratching. On the contrary, in the design of existing conventional robot actuators, it is extremely difficult to open a hole in the middle, and cable exposure will bring many disadvantages.

[0071] 3. This embodiment can achieve a large reduction ratio (the economical reduction ratio range is 30 to 400), which is larger than that of the harmonic reducer (40 - 150), and is also incomparable with the reduction ratio of the conventional multi-stage planetary series reducer.

[0072] 4. The gear module and tooth width in this embodiment are kept the same as those in the first embodiment. Therefore, the strength, load-bearing capacity, and service life of the gears are exactly the same as the advantages in the first embodiment.

[0073] 5. Due to the floating of several planet gears evenly distributed in the circumferential direction, when the planet gears bear the combined torque and force of the internal gear ring and the sun gear, the relative positions of the planet gears can be adjusted adaptively to ensure that the planet gears distributed in the circumferential direction can evenly share the torque and force together, realizing the automatic average distribution of the load between the planet gears, prolonging the service life of the reduction structure, and avoiding the premature failure and life termination of a very small number of planet gears that bear excessive loads due to uneven load distribution.

[0074] On the contrary, in a conventional planetary reducer with a planet carrier, if the positional tolerance of the pin hole of the planet gear is poor, it is necessary to reserve a large meshing backlash for the gears (to prevent gear meshing jamming or seizure). Since the position of the planet gear is restricted by the pin of the planet carrier on the planet carrier and cannot move to achieve automatic compensation, when the planet gear is stressed, the load distribution will be uneven, that is, individual planet gears will bear excessive loads and cause tooth breakage or rapid reduction of life and premature failure due to excessive load, and other individual planet gears will have a meshing suspension phenomenon due to bearing a small load.

[0075] In this embodiment, the main function of the central hole of the planet gear is an assembly process hole (used for circumferential uniform positioning during assembly), and its hole can store grease. There is also a circle of grease storage holes or grooves on the output flange at both end faces and the actuator housing seat to store grease to ensure sufficient grease reserve and full lubrication at the end of the planet gear and the gear meshing part, prolonging the service life of the reduction structure.

[0076] The working principle of the second embodiment is as follows: The motor rotor drives the sun gear to rotate. Since the sun gear meshes with the planet gears, the planet gears revolve under the drive of the sun gear, and the planet gears rotate on their own due to the reaction force of the fixed gear ring. The planet gears drive the output gear ring to rotate, and the output gear ring drives the output flange to rotate.

[0077] As Figure 12 shown, a circle of grease storage grooves or grease storage holes 10 are arranged in a ring on the inner peripheral surface of the output flange 6 or the actuator housing 21.

[0078] The output flange 6 is provided with pin columns and threaded holes for providing external connection and transmitting power.

[0079] The above are only embodiments of the present utility model, and do not thus limit the patent scope of the present utility model. Any equivalent structural transformation made by using the content of the specification and drawings of the present utility model, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present utility model.

Claims

1. A large reduction ratio robot joint actuator with a built-in deceleration structure, characterized in that: It includes two internal gear rings, several planet gears (1), an actuator housing (21) and an actuator cover plate (22). A receiving space is jointly formed between the actuator housing and the actuator cover plate. An electric motor stator (31) and an electric motor rotor (32) are installed inside the receiving space, and the electric motor stator is fixed to the actuator housing; Several of the planet gears are provided inside the two internal gear rings, and the several planet gears are evenly arranged along the circumferential direction of the internal gear rings. Each planet gear meshes with the two internal gear rings and the meshing center distances are kept equal; The two internal gear rings are internal gear rings with the same module but different numbers of teeth. The two internal gear rings are respectively a fixed gear ring (4) and an output gear ring (5). The fixed gear ring is installed on the actuator housing, and the output gear ring is installed on an output flange (6). The planet gears revolve around the central axis of the two internal gear rings under the direct or indirect drive of the electric motor rotor, and the planet gears can rotate around their own central axes.

2. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: The difference in the number of teeth between the fixed gear ring and the output gear ring is equal to the number of planet gears.

3. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: The several planet gears are rotatably connected to a planet carrier (7), and the planet carrier is fixed to the electric motor rotor.

4. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: The teeth on the surface of the planet gear are herringbone teeth (11), and the herringbone teeth are composed of two symmetrically arranged helical teeth.

5. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: A hollow shaft (8) is installed at the center of the actuator, and the hollow shaft is fixed to the output flange.

6. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: A sun gear (9) is installed at the center of the actuator, and the sun gear is fixed to the electric motor rotor. The several planet gears are located between the sun gear and the two internal gear rings, and the several planet gears respectively mesh with the sun gear.

7. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 6, characterized in that: A central through hole (91) is provided at the center of the sun gear.

8. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: A grease storage groove is provided in a circle on the inner peripheral surface of the output flange or the actuator housing, or grease storage holes (10) are arranged in a ring.

9. The large reduction ratio robot joint actuator with an internal reduction structure according to claim 1, characterized in that: The output flange is provided with pin columns and threaded holes for providing external connection and transmitting power.

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