A hydraulic cylinder driven robot joint capable of 720 degree rotation and a torque sensing method thereof

Abstract

The application discloses a 720-degree rotary hydraulic oil cylinder driving robot joint and a torque sensing method thereof, and belongs to the technical field of heavy-load robots and special equipment. The joint comprises a rack, an NGW single-row planetary gear train, a double-mode driving module and a multi-source sensing control module. The application arranges the NGW planetary gear train in a reverse speed-increasing manner, utilizes a short-stroke rack oil cylinder to realize a small swing, achieves bidirectional rotation of an output end of ±360 degrees, and realizes a total of 720-degree non-blind area rotation, thereby solving the problem of restriction of oil cylinder stroke and swing angle; the driving base supports free switching of double-oil-cylinder light weight and four-oil-cylinder heavy load modes, and is suitable for different loads and installation spaces. The application is matched with an oil pressure sensor, torque calculation is realized by relying on oil pressure, stroke and rotation angle multi-source signal fusion algorithm, and a high-priced dynamic torque sensor is saved. The scheme has compact structure, impact resistance and low cost, and can be applied to heavy-load mechanical arms, rotary platforms, special engineering machinery and other heavy-load automatic operation scenes.

Description

Technical Field

[0001] This invention relates to the fields of heavy-duty industrial robots, special engineering machinery, and large-scale automated rotary equipment. Specifically, it relates to a hydraulic cylinder driven robot joint based on NGW single-row planetary gear train reverse speed-increasing transmission. In particular, it relates to a hydraulic joint mechanism and a high-precision real-time torque sensing and control method that is compatible with both dual-cylinder and four-cylinder drive configurations. Relying on the fusion of multi-source data such as hydraulic pressure, stroke, and encoder, it can achieve ±360° full coverage, 720° full-range rotation, and stable high torque output without the need for a high-precision dedicated torque sensor. Background Technology

[0002] Currently, the mainstream electromechanical drive solution for heavy-duty robot rotary joints uses servo motors paired with RV reducers or planetary reducers. This type of solution generally suffers from inherent defects such as low torque output limit, weak impact resistance, poor short-term overload performance, and lack of self-locking function after power failure, making it difficult to adapt to heavy-duty, impact-prone, and continuous load operation scenarios. Hydraulic drive joints, with their advantages of high power density, high overload ratio, excellent self-locking performance, and strong environmental adaptability, have become the core development direction for heavy-duty rotary joints. However, existing hydraulic heavy-duty robot joints still have several key technical shortcomings, which seriously restrict the large-scale promotion and application in the industry. The existing hydraulic heavy-duty robot joints have the following specific technical defects: (1) Fixed drive configuration and poor adaptability to different scenarios. Most existing hydraulic joints adopt a fixed single-cylinder or four-cylinder drive structure, which cannot flexibly switch the drive layout according to the load level and installation space. Under low load conditions, the four-cylinder drive has redundant resources and high energy consumption. The four-cylinder layout cannot be adapted to small and lightweight installation scenarios, resulting in extremely poor flexibility of use. (2) Uneven driving force and short component life. Traditional hydraulic joints use single cylinder or symmetrical double cylinder single-point or two-point drive, with a single driving point and the load concentrated in the local meshing area, resulting in uneven circumferential force on the planetary carrier and excessive local contact stress. This not only limits the upper limit of joint torque output, but also easily causes component failure problems such as tooth surface wear, tooth breakage, and rack deformation. (3) Torque, swing angle and volume cannot be balanced. In conventional heavy-duty swing joint structures, the driving torque, rotation angle and overall volume are mutually restrictive. If the torque and swing angle parameters are increased, the cylinder stroke and cylinder diameter must be increased, which cannot meet the requirements of flat, compact and low-cost integrated installation of heavy-duty equipment. (4) Large-angle rotation depends on ultra-long cylinder stroke. Traditional rack and pinion direct-drive hydraulic joints have no angle amplification structure, and the linear stroke of the cylinder directly determines the maximum swing angle of the joint. In order to achieve ±360° ultra-large angle bidirectional rotation, a customized ultra-long stroke cylinder needs to be configured, which is not only difficult to process and has high manufacturing cost, but also has problems such as high risk of sealing oil leakage and slow dynamic response, which severely limits the applicable scenarios. (5) High cost and poor accuracy and stability of torque sensing. Currently, most high-precision heavy-duty joints are equipped with imported special high-torque dynamic sensors to collect load data. These sensors are expensive, have weak vibration resistance, and poor adaptability to harsh environments. Some equipment relies on motor current to indirectly estimate torque, which is greatly affected by transmission backlash, elastic deformation, and oil pressure pulsation. This results in problems such as sensing lag and high steady-state error, making it difficult to meet the requirements of high-precision closed-loop control. (6) The system has low stiffness and poor running stability. Under conditions of large inertia load, high frequency start-stop and frequent reversing, the transmission chain of the single-point and two-point fixed drive structure is prone to periodic torsional vibration and radial yaw, resulting in insufficient motion stability and inability to achieve high-precision force-position coordination control. In summary, the industry currently lacks a heavy-duty hydraulic robot joint that can flexibly switch between dual and quadruple cylinders, achieve ±360° (720°) full-range rotation using short-stroke cylinders, possess high sensing accuracy, low production cost, and strong operational reliability. Based on this, this invention combines the speed-increasing characteristics of the NGW planetary gear system, a multi-mode distributed drive structure, and a low-cost load sensing algorithm to develop a novel hydraulic joint, addressing the aforementioned industry pain points. Summary of the Invention

[0003] 3.1 Purpose of the Invention To address the shortcomings of existing heavy-duty hydraulic robot joints, such as fixed joint drive modes, limited rotation angles, excessive cylinder stroke, high torque sensing costs, concentrated force, and poor system stability, this invention provides a hydraulic cylinder-driven robot joint capable of 720-degree rotation and its torque sensing method. The core of this invention relies on the reverse speed-increasing characteristics of an NGW single-row planetary gear system to construct an angle amplification mechanism. It designs a universal integrated mounting structure compatible with lightweight dual-cylinder and heavy-duty four-cylinder configurations, adapting to different loads and installation scenarios. Embedded hydraulic pressure sensors are configured in the independent oil chambers of each cylinder to improve sensing sensitivity, eliminating the need for high-cost dedicated high-torque sensors. By integrating three basic low-cost signals—cylinder hydraulic pressure, piston stroke, and spindle encoder—high-precision torque calculation and closed-loop control are achieved. This significantly improves the joint's operational stability and detection accuracy under complex working conditions while reducing production costs. 3.2 Technical Solution To achieve the above objectives, the present invention provides a hydraulic cylinder-driven robot joint capable of 720-degree rotation, comprising a frame, a planetary gear system module, a drive module, and a sensing and control module. The planetary gear train module is a standardized single-row NGW-type planetary transmission structure, which is the core component for achieving short-stroke, large-angle output. It includes an external gear ring, a central gear, several planet gears, and a disc-type planet carrier. The external gear ring has an internal gear structure and is fixedly installed inside the frame as an absolute fixed reference. The planet gears are correspondingly mounted on the outer side of the planet shafts of the planet carrier through heavy-duty bearings. The central gear is located at the center of the planetary gear train and is supported on the frame by the rotation of the main shaft, forming the joint power output end. The planet carrier can rotate freely relative to the frame, serving as the power input component of the planetary gear train. The drive module adopts a modular design, which is compatible with two interchangeable drive configuration modes. The installation interface and control logic of the two modes are completely unified. They can be flexibly selected according to the load level and installation space, without conflict and with strong adaptability. Mode 1, Dual-cylinder lightweight drive mode: Configured with two short-stroke rack cylinders of the same specifications. The two cylinders are symmetrically arranged opposite each other at 180° along the same radial diameter of the planetary carrier. It is suitable for medium and small loads and narrow installation space scenarios. The structure is simplified and the energy consumption is lower. Mode 2, Four-cylinder heavy-duty drive mode: Configure four short-stroke rack cylinders of the same specifications, divided into two independent drive units; the first group of two rack cylinders are arranged opposite each other at 180° along the first diameter direction of the planetary carrier, and the second group of two rack cylinders are arranged opposite each other at 180° along the second diameter direction of the planetary carrier. The included angle between the axes of the two groups of cylinders is preferably 90°, which is suitable for ultra-large load conditions, realizes multi-point load distribution, and improves the overall rigidity of the system. The planetary carrier has an integrally machined drive gear ring on its outer edge. The output racks of the dual or quad cylinders mesh with the drive gear ring. Through the coordinated differential extension and retraction of the cylinders, the planetary carrier is driven to perform small-angle limited reciprocating oscillation. The drive requirements can be met by using short-stroke cylinders throughout the process, which reduces the difficulty of cylinder machining and the risk of seal failure from the source. The planetary gear system adopts a dedicated reverse-increase output angle working mode. The working logic is that the outer gear ring is fixed and locked, the planet carrier is actively input at low speed and small angle, and the center gear is driven output at a large angle. The transmission ratio (the reduction ratio of the center gear driving to the planet carrier) is calculated as follows: ic-s=ns / nc=(Zs+Zr) / Zs; where ic-s is the overall transmission ratio, ns is the speed of the center gear, nc is the speed of the planet carrier, Zs is the number of teeth of the center gear, and Zr is the number of teeth of the outer gear ring. Since the number of teeth of the outer gear ring Zr is always greater than the number of teeth of the center gear Zs, according to the speed increase (the speed ratio of the planet carrier input to the center gear output, the speed ratio of the planet carrier to the center gear driving), the transmission ratio is-c=nc / n<1 is formed, which forms a constant speed increase amplification structure. This can multiply the small swing angle of the planet carrier, and achieve ±360° full coverage and a total of 720° continuous bidirectional rotation at the output end with the small linear stroke of the hydraulic cylinder, effectively improving the joint response speed. The perception and control module abandons traditional high-cost dedicated high-torque dynamic sensors, and consists only of an embedded pressure sensor, a built-in stroke sensor, a high-precision absolute encoder, and a hydraulic-electric control unit. Each rack cylinder has an embedded high-frequency pressure sensor in its independent oil chamber for collecting high-precision oil pressure data. Each rack cylinder also has a built-in stroke sensor to collect real-time piston extension and retraction stroke and position status. A high-precision absolute encoder is coaxially mounted at the end of the central wheel spindle to collect real-time rotation angle and speed data. All sensing components are electrically connected to the hydraulic-electric control unit, and relying on a multi-source, low-cost signal fusion algorithm, high-precision torque calculation and force-position closed-loop control are achieved without a dedicated torque sensor. Furthermore, the maximum swing angle of the planetary carrier is limited to within ±110°, and can be driven by a short-stroke rack and pinion cylinder. Relying on the NGW planetary gear system's adjustable speed ratio of 3.4 to 3.8, the small input swing angle of ±110° of the planetary carrier can be amplified into a complete rotation angle of ±360° at the output end, and the total rotation angle of the whole machine can reach 720°. There is no need to configure an ultra-long stroke cylinder, and the structural compactness is greatly improved. Furthermore, the rack cylinder adopts a differential oil supply control method, with the opposing cylinders working synchronously, which can completely cancel the radial component force on one side, retaining only the circumferential driving torque, effectively improving the running stability and transmission accuracy of the planetary carrier. The second aspect of this invention provides a method for real-time joint torque sensing of a heavy-duty hydraulically driven robot, adaptable to both dual-cylinder and four-cylinder driving modes, without requiring a high-precision dedicated high-torque sensor. Specifically, it includes the following steps: S1. Multi-source data synchronous acquisition: The hydraulic control unit synchronously calls multiple embedded pressure sensors and built-in stroke sensors to collect high-precision hydraulic pressure data of each rack cylinder in the corresponding drive mode and real-time extension and retraction stroke position data of the piston. The hydraulic pressure data is filtered and noise-reduced to improve the signal-to-noise ratio. At the same time, the real-time angular position and speed data of the center wheel are collected through a high-precision absolute encoder. S2. Single-cylinder driving force calculation: Based on the oil pressure difference between the inner and outer oil chambers of the cylinder and the effective pressure area of ​​the piston, the original output thrust of a single rack is calculated. At the same time, a deviation compensation coefficient is added in combination with the real-time stroke position of the piston to correct the thrust error caused by piston off-center load and oil compressibility, thereby improving the thrust calculation accuracy. S3. Input torque synthesis: Based on the current dual-cylinder or four-cylinder drive mode of the equipment, combined with the pitch circle radius of the drive gear ring, the circumferential drive torque of each group of cylinders is superimposed to accurately solve the real-time input torque of the planetary carrier. S4. Output torque calculation: Combining the fixed reverse speed-increasing transmission ratio of the NGW planetary gear system, and matching gear meshing loss, bearing friction loss, and angular position compensation parameters, the real-time load torque at the output end of the center wheel is accurately calculated. S5. Force and position closed-loop control: The electronic control unit compares the real-time torque and angle parameters with the preset target parameters, and dynamically adjusts the oil supply pressure and extension stroke of each group of oil cylinders to achieve high-precision coordinated control of torque and position through dual closed-loop control. 3.3 Beneficial Effects Compared with the prior art, the present invention has the following significant advantages: (1) Achieving a large swing angle with a short stroke, breaking through structural constraints. This invention innovatively adopts the reverse speed-increasing working logic of the NGW planetary gear system, using a short-stroke rack and pinion cylinder to drive the planetary carrier to swing slightly. After being amplified by 3.4 to 3.8 times the angle, it achieves a bidirectional full coverage of ±360° at the output end and a total continuous rotation of 720°. This completely solves the industry pain point that traditional hydraulic joints require an ultra-long cylinder stroke to achieve a large angle of rotation, significantly reduces the axial dimension of the cylinder, and lowers the costs of cylinder processing, sealing, and subsequent maintenance. (2) Dual-mode compatibility and full-scenario coverage. The drive module of this invention adopts a modular combination design, which can freely switch between two working modes: dual-cylinder lightweight and four-cylinder heavy-duty. The dual-cylinder mode has a simplified structure and lower energy consumption, and is suitable for small and medium loads and narrow installation spaces. The four-cylinder mode has multiple load distribution, high torque limit and strong system rigidity, and is suitable for ultra-large load conditions. The interfaces and control logic of the two modes are universal, and there is no need to modify the machine structure. The scope of scenario adaptation is extremely wide. (3) No dedicated torque sensor required, resulting in cost reduction and high reliability. This invention abandons the expensive, poorly vibration-resistant, and easily damaged dedicated high-torque dynamic sensor, and integrates three types of low-cost and high-reliability sensing signals: high-precision hydraulic pressure, piston stroke, and spindle rotation angle. Through multi-source data fusion algorithm, errors such as transmission backlash, elastic deformation, and friction loss are compensated to achieve high-precision torque calculation. Compared with traditional solutions, the overall hardware cost is reduced by 15% to 30%, and the basic sensor has a high protection level, is shock-resistant, and vibration-resistant, making it suitable for harsh heavy-duty working conditions such as mines, construction sites, and outdoor environments. (4) Multi-point load sharing and strong ultra-large torque output capability. The four-cylinder heavy-duty mode adopts a 90° distributed symmetrical drive structure, and the four power sources act synchronously on the drive gear ring to achieve multi-point uniform load sharing. It can significantly improve the rated output torque of the joint without increasing the cylinder diameter or lengthening the cylinder stroke. The dual-cylinder mode takes into account the cost and performance of conventional heavy-duty scenarios, reduces the difficulty of cylinder design and manufacturing, and extends the service life of seals. (5) Highly integrated structure with excellent adaptability. This invention adopts a multi-point distributed short-stroke drive structure to replace the traditional large-diameter, long-stroke single-cylinder drive structure. Standardized small-specification short-stroke hydraulic cylinders can meet the requirements of heavy load and large swing angle. The overall size of the machine is greatly reduced, the layout is neat, and it can be adapted to embedded installation scenarios in narrow spaces. (6) The system has high rigidity and good running stability. The dual-cylinder 180° opposed drive and four-cylinder 90° four-way symmetrical drive structure can effectively constrain the planetary carrier's yaw and torsional degrees of freedom, greatly improve the overall torsional rigidity of the joint, and effectively suppress the torsional vibration phenomenon during the start-stop and reversing process of large inertia loads. Combined with the stroke-hydraulic dual feedback control logic, it significantly improves the joint's motion stability and positioning and torsion control accuracy. (7) Extend the service life of transmission components. The multi-point symmetrical meshing structure can evenly distribute the contact stress on the tooth surface, avoid local stress concentration, and reduce the wear rate of the drive gear ring, planetary gear, and cylinder rack; at the same time, the symmetrical drive structure can offset most of the radial force, reduce the lateral load on the bearing, and combined with the load distribution characteristics of the NGW planetary gear system, comprehensively improve the fatigue service life of the whole machine. (8) Hydraulic self-locking safety and low failure rate. The hydraulic drive structure can achieve a short-term overload ratio of more than 2 times, and its impact resistance and overload resistance performance far exceed those of electromechanical deceleration schemes; after the equipment is powered off and stopped, it can rely on oil pressure to maintain pressure and self-lock, without the need for additional electromagnetic brake devices, reducing the number of equipment failure points and further reducing the overall production and maintenance costs. Attached Figure Description

[0004] Figure 1 This is a three-dimensional schematic diagram of the overall structure of the present invention; Figure 2 This is a simplified diagram of the reverse speed-increasing motion of the NGW-type planetary gear train of the present invention (outer gear ring fixed, planet carrier input, center gear output); Figure 3 This is a comparative analysis diagram of the force distribution of the dual-cylinder and four-cylinder distributed drive systems of the present invention; Figure 4 This is a block diagram illustrating the principle of multi-channel hydraulic and multi-source sensing control in this invention. Explanation of reference numerals in the attached diagram: 1-Frame, 2-External gear ring, 3-Center wheel, 4-Main shaft, 5-Planet carrier, 6-Planet shaft, 7-Planet gear, 8-Drive gear ring, 9-Rack and pinion cylinder, 9a-First group of cylinders, 9b-Second group of cylinders, 10-Rack, 11-Embedded pressure sensor, 12-High-precision absolute encoder, 13-Built-in stroke sensor. Detailed Implementation

[0005] The technical solution of the present invention will be fully and clearly described below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. 5.1 Example 1 (Optimal heavy-duty example, four-cylinder drive, 720° full-range rotation) A hydraulic cylinder-driven robot joint capable of 720-degree rotation includes a frame 1, an external gear ring 2 with an internal gear structure fixedly embedded inside the frame 1, a center wheel 3 arranged at the center of the whole machine and interference-fitted on the outside of the main shaft 4, and the two ends of the main shaft 4 are supported on the frame 1 by heavy-duty bearings, forming the power output end of the equipment. The disc-shaped planetary carrier 5 is movably assembled inside the frame 1. Three planetary shafts 6 are evenly arranged around the planetary carrier 5. Three planetary gears 7 are correspondingly fitted to the outside of the planetary shafts 6 through heavy-duty bearings. The inner side of the planetary gears 7 meshes with the central gear 3, and the outer side meshes with the fixed external gear ring 2, forming a standardized single-row NGW planetary gear system. In this embodiment, the planetary gear system adopts a reverse speed-increasing working mode throughout the entire process. The drive module adopts a dual-group, four-cylinder, short-stroke drive structure, configured with four identical short-stroke rack cylinders 9, divided into two groups. The first group of cylinders 9a contains two cylinders, arranged opposite each other at a 180° angle along the transverse diameter of the planetary carrier 5. The second group of cylinders 9b contains two cylinders, arranged opposite each other at a 180° angle along the longitudinal diameter of the planetary carrier 5. The two groups of cylinders are perpendicular to each other and arranged in a 90° ring. The outer edge of the planetary carrier 5 is integrally machined with a drive gear ring 8. The output racks 10 of the four cylinders simultaneously mesh with the outer side of the drive gear ring 8, achieving multi-point coordinated drive. The force comparison analysis of the dual-cylinder and four-cylinder distributed drive is as follows. Figure 3 As shown, the arrow indicates the direction of the hydraulic cylinder's driving force. In this embodiment, the preferred tooth parameters for the planetary gear train are: external gear ring teeth Zr=100, central gear teeth Zs=40; the transmission ratio ic-s=(40+100)÷40=3.5 is calculated according to the reverse speed-increasing formula, and the angle magnification factor is 3.5 times. Relying on this magnification characteristic, the planetary carrier can be driven to complete a small reciprocating oscillation of ±103°, thereby achieving a complete bidirectional rotation of ±360° for the central gear. The total rotation angle of the entire machine reaches 720°, with no angle blind spot. The entire process does not require an ultra-long stroke cylinder, completely avoiding the defects of easy seal damage and slow response of long stroke cylinders. The sensing and control module adopts a multi-source sensing scheme without dedicated torque sensors: each of the four rack and pinion cylinders 9 has an embedded pressure sensor 11 embedded in its dual chamber to simultaneously collect eight channels of high-precision hydraulic pressure data; each cylinder has a built-in stroke sensor 13 to collect four channels of piston extension and retraction position data in real time; and a 19-bit high-precision absolute encoder 12 is mounted at the end of the main shaft 4 to collect the output angle and speed signals. The electronic control unit corrects the meshing deviation with the stroke data, solves the original thrust of the cylinder with the stabilized hydraulic pressure data, and accurately calculates the output torque after deducting transmission friction losses by combining the encoder angle signal and a 3.5 times transmission ratio. The torque sensing error is ≤±1.5%, and the rated output torque of the joint can reach 220kN·m, making it suitable for ultra-heavy-duty operation scenarios. 5.2 Example 2 (Lightweight Example, Dual-Cylinder Drive, Medium and Small Load Conditions) The overall structure, planetary gear train parameters, and torque sensing method of this embodiment are basically the same as those of Embodiment 1. The difference lies in the fact that the drive module adopts a single-set opposed dual-cylinder drive mode. This embodiment only configures two short-stroke rack cylinders 9, symmetrically arranged along the planetary carrier 5 with a single radial diameter of 180°. They are directly assembled using a universal mounting base, without the need to modify the frame and transmission structure. The two cylinders have a total of four independent oil chambers, each equipped with an embedded pressure sensor 11 to complete the oil pressure data acquisition. The transmission ratio of this embodiment is 3.5 times, and a small swing of ±103° of the planetary carrier can achieve a full-range rotation of 720° at the output end. The overall structure is simplified, the weight is lower, and the energy consumption is lower, making it suitable for narrow installation spaces and small to medium load rotation conditions within 50kN·m. 5.3 Example 3 (High-Frequency Heavy-Load Optimization Example) This embodiment is an optimized upgrade based on the four-cylinder heavy-duty drive mode. The structure is basically the same as in Embodiment 1, but the gear ratio of the NGW planetary gear train is adjusted: the number of teeth on the outer ring gear Zr=110, and the number of teeth on the central gear Zs=40, increasing the transmission ratio to 3.75 times. Only a small ±96° oscillation of the planetary carrier is needed to achieve a complete ±360° rotation of the central gear, totaling 720°. This requires a shorter cylinder stroke and faster drive response, effectively adapting to heavy-duty rotary conditions with high-frequency start-stop and frequent reciprocating reversals, further improving operating efficiency and stability. 5.4 Example 4 (Low-cost multi-source fusion torque sensing example) This embodiment is based on the above-mentioned dual-cylinder and four-cylinder drive modes, and adopts a high-precision torque sensing method without a dedicated torque sensor. The specific steps are as follows: S1. Multi-source data synchronous acquisition: Each cylinder's independent oil chamber acquires high-precision oil pressure data through an embedded pressure sensor 11, which is then filtered and optimized for noise reduction; the built-in stroke sensor 13 synchronously acquires piston extension and retraction position data; the high-precision absolute encoder 12 acquires spindle angular displacement and speed data in real time, realizing synchronous sampling and transmission of the three types of signals. S2. Thrust Calculation: The original thrust of the hydraulic cylinder is calculated using the formula F=P1·A-P2·A, where P1 and P2 are the hydraulic pressures of the two chambers of the hydraulic cylinder, and A is the effective pressure area of ​​the piston. A dynamic compensation coefficient is added in combination with the real-time stroke position of the piston to correct the thrust error caused by hydraulic compression and rack off-center loading. S3. Input torque synthesis: Based on the equipment drive mode, combined with the pitch circle radius of the drive gear ring 8, and superimposed with the circumferential drive torque of the corresponding hydraulic cylinder group, the real-time input torque of the planetary carrier 5 is accurately calculated. S4. Output torque conversion: Combining the fixed speed ratio of the NGW planetary gear system, and deducting the inherent losses of gear meshing and bearing friction, the real-time load torque at the output end of the center gear 3 is accurately calculated. S5. Closed-loop control: The electronic control unit dynamically allocates the oil supply pressure and extension stroke of each group of hydraulic cylinders according to the real-time torque and angle signals obtained by calculation, so as to realize precise and coordinated control of joint torque and position through dual closed-loop control.

Claims

1. A hydraulic cylinder-driven robot joint capable of 720-degree rotation, characterized in that, Includes a frame (1), a planetary gear train module, a drive module, and a sensing and control module; The planetary gear train module is a standardized single-row NGW type planetary transmission structure, including an external gear ring (2), a central gear (3), several planet gears (7) and a planet carrier (5); the external gear ring (2) is an internal gear ring and is fixedly installed on the inner side of the frame (1); the central gear (3) is rotatably supported at the center position of the frame (1) through the main shaft (4); the planet gears (7) are mounted on the planet shafts (6) of the planet carrier (5); the planet carrier (5) can rotate relative to the frame (1); The drive module adopts a universal mounting base structure, which is compatible with two interchangeable drive configuration modes and can be flexibly selected according to the load level and installation space. The drive module includes several short-stroke rack cylinders (9) of the same specifications. The outer edge of the planetary carrier (5) is fixedly provided with a drive gear ring (8). The output racks (10) of all rack cylinders (9) mesh with the drive gear ring (8) to cooperate in driving the planetary carrier (5) to perform small-angle limited reciprocating swing. Each rack cylinder (9) has two independent sealed oil chambers inside, and each independent oil chamber is equipped with an independent pressure sensor to collect pressure signals; The planetary gear system adopts a reverse speed-up working mode, with the external gear ring (2) as the fixed reference, the planet carrier (5) as the power input component, and the center gear (3) as the power output component. Relying on the angle amplification characteristics of the NGW planetary gear system, the small swing angle of the planet carrier is amplified into a large angle rotation at the output end. The sensing and control module includes an embedded pressure sensor (11), a built-in stroke sensor (13), a high-precision absolute encoder (12), and a hydraulic electronic control unit. The sensing and control module abandons the dedicated high-torque dynamic sensor and calculates the load torque by fusing multi-source data such as oil pressure, piston stroke, and rotation angle to complete closed-loop control.

2. A hydraulic cylinder-driven robot joint capable of 720-degree rotation according to claim 1, characterized in that, The two interchangeable driver configuration modes of the driver module are as follows: Mode 1, Lightweight Drive Mode: Two rack cylinders (9) are configured, and the two cylinders are arranged opposite each other at 180° along the same radial diameter of the planetary carrier (5), which is suitable for small and medium loads and narrow installation space scenarios; Mode 2, Heavy-duty drive mode: Four rack cylinders (9) are configured and divided into two groups. The first group of cylinders (9a) are arranged opposite each other at 180° along the first diameter direction of the planetary carrier (5), and the second group of cylinders (9b) are arranged opposite each other at 180° along the second diameter direction of the planetary carrier (5). The first diameter and the second diameter are perpendicular to each other. The two groups of cylinders are distributed in a 90° ring, which is suitable for ultra-large load operation scenarios. The two drive modes have completely unified installation interfaces and control logic, requiring no modification to the frame (1) and planetary gear module, and can be freely switched without conflict.

3. A hydraulic cylinder-driven robot joint capable of 720-degree rotation according to claim 1, characterized in that, The formula for calculating the reverse speed-increasing transmission ratio of the NGW planetary gear system is ic-s=ns / nc=(Zs+Zr) / Zs; where Zs is the number of teeth of the central gear (3) and Zr is the number of teeth of the outer gear ring (2), and Zr>Zs, the transmission ratio ic-s<1, forming a fixed angle amplification structure.

4. A hydraulic cylinder-driven robot joint capable of 720-degree rotation according to claim 1, characterized in that, The maximum swing angle of the planetary carrier (5) is limited to ±110°. Combined with the NGW planetary gear system with an adjustable speed ratio of 3.4 to 3.8 times, the center gear (3) can achieve ±360° bidirectional blind-spot rotation, with a total rotation angle of 720°.

5. A hydraulic cylinder-driven robot joint capable of 720-degree rotation according to claim 1, characterized in that, The embedded pressure sensor (11) is a high-frequency pressure sensor. Each rack cylinder (9) has an embedded pressure sensor (11) integrated inside its independent oil chamber for synchronously collecting high-precision oil pressure data.

6. A hydraulic cylinder-driven robot joint capable of 720-degree rotation according to claim 1, characterized in that, Each rack cylinder (9) is equipped with a built-in stroke sensor (13) to collect piston extension and retraction stroke and position data in real time and compensate for transmission deviations in torque calculation process; the high-precision absolute encoder (12) is coaxially fixedly installed at the end of the main shaft (4) to collect the angular displacement and speed signals output by the center wheel (3) in real time.

7. A real-time torque sensing method for a hydraulic cylinder-driven robot joint capable of 720-degree rotation, based on any one of claims 1 to 6, characterized in that, No dedicated high-torque dynamic sensor is required; it is compatible with both dual-cylinder and four-cylinder drive modes and includes the following steps: S1. Multi-source data synchronous acquisition: The hydraulic control unit synchronously acquires the dual-chamber oil pressure data and piston stroke position data of the rack cylinder (9) in the corresponding drive mode through the embedded pressure sensor (11) and the built-in stroke sensor (13). The oil pressure data is filtered and optimized for noise reduction. The real-time angular position data of the center wheel (3) is acquired through the high-precision absolute encoder (12). S2. Single-cylinder thrust calculation: Based on the oil pressure difference in the cylinder cavity and the effective pressure area of ​​the piston, the original thrust of the cylinder is calculated, and a compensation coefficient is added in combination with the real-time stroke position of the piston to correct the transmission deviation caused by piston off-center load and oil compression. S3, Input torque synthesis: Based on the actual selected drive mode, combined with the pitch circle radius of the drive gear ring (8), the corresponding circumferential drive torque of the oil cylinder is superimposed to solve the real-time input torque of the planetary carrier (5); S4. Output torque conversion: Combining the fixed reverse speed-increasing transmission ratio of the NGW planetary gear system, deducting gear meshing and bearing friction losses, the real-time working load torque of the output end of the center wheel (3) is calculated. S5, Force-position closed-loop control: The electronic control unit compares the real-time torque, angle and preset target value, and dynamically adjusts the oil supply pressure and extension stroke of each set of rack cylinders (9) to complete the precise control of torque and position through a double closed loop.

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