Hydraulically driven rigid-flexible coupling robot arm

Abstract

This invention discloses a hydraulically driven rigid-flexible coupled robotic arm. Through the synergistic action of a retractable constraint layer, limiting structural components, and an axial preload return component, the robotic arm establishes a stable and recognizable correspondence between the volume input and bending output of the hydraulic drive cavity, improving the centering capability after unloading and the consistency of repeatable positioning. During operation, the rigid hydraulic robotic arm structure is first controlled to complete macroscopic positioning. Then, based on the volume-pressure-attitude recognition of the flexible joint unit, the hydraulic power unit is coordinated and controlled. Depending on the target attitude, a single-branch independent drive, a dual-branch differential drive, or a three-branch synchronous drive mode is selected to achieve deflection in the corresponding bending plane, bending in the synthetic direction, and compliant adjustment under axial elongation or near-linear attitudes, respectively. This invention combines high-load macroscopic operation capability, compliant operation capability in confined spaces, and high end-effector positioning accuracy, making it suitable for precision operations in underwater exploration, deep-sea sampling, and unstructured environments.

Description

Technical Field

[0001] This invention relates to a coupled robotic arm, and relates to the fields of robotics and fluid drive control, specifically to a hydraulically driven rigid-flexible coupled robotic arm. Background Technology

[0002] Traditional rigid hydraulic robotic arms have advantages such as large load capacity, fast response and high positioning accuracy, enabling them to complete large-scale, high-load underwater operations; however, their high structural rigidity and poor environmental adaptability make them prone to damage when contacting fragile targets such as seabed artifacts and biological samples, and they are difficult to perform compliant operations in confined and unstructured spaces.

[0003] Although existing flexible actuators have good compliance, under hydraulic drive conditions, traditional pure hydraulic drive cavities are prone to significant radial expansion, residual deformation after unloading, and mutual interference between branches. This results in a lack of stable correspondence between the bending angle and the input volume, making it difficult to meet the requirements of engineering applications in terms of repeatability and attitude maintenance accuracy.

[0004] Furthermore, existing rigid-flexible coupling solutions mostly focus on physically connecting a rigid robotic arm to a flexible end effector, lacking structural and control design considerations based on the controllable deformation characteristics of the flexible end effector. Control often involves only unified drive or simple closed-loop correction, failing to establish a model to identify the relationship between the input volume of the flexible branch, cavity pressure changes, and the end effector's posture. This makes it difficult to achieve high-precision collaborative operation of "coarse positioning of the rigid robotic arm and fine adjustment of the flexible joint." Therefore, an integrated solution that balances the structural stability of the flexible joint, the discernibility of input and output, and the accuracy of rigid-flexible collaborative control is urgently needed. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention provides a hydraulically driven rigid-flexible coupled manipulator. This invention is an underwater operation equipment that integrates a rigid hydraulic manipulator and an end-effector parallel flexible joint unit into a single hydraulic power supply architecture. It improves end-effector positioning accuracy through parameter identification and feedforward-feedback composite control, targeting applications such as deep-sea artifact retrieval, underwater biological sample collection, and confined space exploration. The manipulator uses a three-degree-of-freedom rigid hydraulic manipulator as a macroscopic positioning carrier, integrating a single-section parallel flexible joint unit at its end. Through unified hydraulic power supply, parameter identification, and feedforward-feedback composite control, it achieves precise end-effector attitude adjustment and compliant operation, solving the problems of insufficient control accuracy and poor repeatability in existing rigid-flexible coupling solutions that only achieve physical assembly.

[0006] The technical solution adopted in this invention is: I. A hydraulically driven rigid-flexible coupled robotic arm: The rigid-flexible coupling manipulator includes a rigid manipulator structure, a flexible joint unit equipped with an axial preload return component and a motion capture calibration ball, a connector, and a hydraulic power unit. The root end of the rigid manipulator structure is mounted in a fixed position, and the root end of the flexible joint unit is mounted at the end of the rigid manipulator structure via the connector. An end effector is mounted at the end of the flexible joint unit. The hydraulic power unit connects the rigid manipulator structure and the flexible joint unit to provide a hydraulic power source. The rigid manipulator structure performs macroscopic positioning near the underwater target area and provides the overall manipulator with a large working space, high load capacity, and stable base attitude. The flexible joint unit performs fine-tuning of the end effector through the axial preload return component and the motion capture calibration ball to perform integrated operations on the underwater target via the end effector. The flexible joint unit is used to complete fine-tuning of the end effector attitude, compliant contact, and fine operations in confined spaces. When the end effector is a flexible gripper, the drive circuit of the flexible gripper is connected in parallel to the volume control branch of the hydraulic power unit for independent control.

[0007] The flexible joint unit further includes a top connector, a bottom connector, several hydraulically driven flexible components installed between the top and bottom connectors, several limiting structures, and two fixed supports. The top and bottom connectors are arranged parallel and spaced apart when the flexible joint unit is in a straight line state. Each hydraulically driven flexible component is evenly spaced circumferentially and its two ends are respectively connected to the opposite side of the top and bottom connectors. Each limiting structure is evenly spaced axially along the flexible joint unit and is not connected to the top and bottom connectors. The axial pre-tightening return components are spaced at the center of each hydraulically driven flexible component and its two ends are respectively connected to the center of the opposite side of the top and bottom connectors. The two fixed supports are respectively fitted onto the outer periphery of the top and bottom connectors. Every two motion capture calibration balls form a ball group. Several ball groups are evenly spaced circumferentially on each fixed support. The two motion capture calibration balls in each ball group are respectively installed on the fixed support on the side closer to and farther away from the flexible joint unit. The top connector is installed at the end of the rigid robotic arm structure through a connector.

[0008] The top connector has three evenly spaced ball groups mounted on its fixed bracket, and the bottom connector has four evenly spaced ball groups mounted on its fixed bracket.

[0009] The top connector and the bottom connector each have a spiral groove at the center of their opposite sides. The spiral groove extends continuously along the circumference and does not extend beyond the other side of the top connector and the bottom connector. The axial preload return member is a helical spring arranged along the central axis of the flexible joint unit. The two ends of the axial preload return member are respectively spirally connected in the spiral groove. The end of the axial preload return member is screwed into the spiral groove to provide axial preload force and unloading return force for unilateral drive of the flexible joint unit, while reducing residual deformation and improving repeatability and consistency.

[0010] The top connector has several connecting bosses with centrally located through holes evenly spaced along the circumference on the side facing the bottom connector. Each connecting boss has a threaded hole on the other side of the top connector, coaxial with and connected to the through hole of its respective connecting boss. A quick connector is connected to each threaded hole, thereby connecting to the hydraulic power unit. The bottom connector has several connecting bosses evenly spaced along the circumference on the side facing the top connector, each connecting boss being coaxial with its respective connecting boss. Each hydraulically driven flexible component includes a retractable constraint layer, two clamps, and a hydraulic drive cavity. The retractable constraint layer is coaxially fitted over the outside of the hydraulic drive cavity. The two ends of the hydraulic drive cavity are respectively fitted onto the connecting bosses of the top connector and the connecting bosses of the bottom connector, thereby connecting to the quick connector. The two clamps are respectively fitted onto the outer circumference of the two ends of the retractable constraint layer, thereby clamping the two ends of the retractable constraint layer and the hydraulic drive cavity together onto the connecting bosses.

[0011] The limiting structure is sheet-shaped, and each limiting structure has circumferential limiting holes and central limiting holes for passing through each expandable constraint layer and axial pre-tightening return component. Each limiting structure is evenly spaced and fitted onto each expandable constraint layer and axial pre-tightening return component to limit the radial expansion of the expandable constraint layer and the relative radial displacement between adjacent expandable constraint layers, so that the fluid volume change is preferentially converted into axial expansion and bending deformation.

[0012] The rigid robotic arm structure includes a base, an upper arm, a lower arm, a lower arm hydraulic cylinder, an upper arm hydraulic cylinder, and a shoulder hydraulic cylinder. The base is installed in a fixed position. The base, upper arm, and lower arm are connected in series and hinged. The base and upper arm are hinged together by a connecting bracket. One end of the connecting bracket is hinged to the end of the base. The cylinder body of the shoulder hydraulic cylinder is located in the base, and its root end is synchronously connected to the hinge position between the connecting bracket and the base via a pin. This allows one end of the connecting bracket to rotate about the vertical joint axis of the shoulder joint at its hinge position with the base. The other end of the connecting bracket is synchronously connected to the root end of the upper arm via a hinged connecting rod. The cylinder body of the upper arm hydraulic cylinder is located in the upper arm, and its root end is hinged to the base via a pin. In the middle of the boom, the end piston rod of the boom hydraulic cylinder is synchronously connected to the hinge position of the connecting bracket and the connecting rod via a pin, allowing the boom to rotate around the horizontal joint axis of the boom joint at the hinge position of the connecting bracket and the connecting rod. The cylinder body of the forearm hydraulic cylinder is located in the middle of the boom, and its root end is hinged to the middle of the boom via a pin. The end piston rod of the forearm hydraulic cylinder is synchronously connected to the hinge position of the boom and the forearm via a pin, allowing the forearm to rotate around the horizontal joint axis of the forearm joint at its hinge position with the boom. A flexible joint unit is installed at the end of the forearm via a connector. The forearm hydraulic cylinder, the boom hydraulic cylinder, and the shoulder hydraulic cylinder are connected. Angle encoders are installed at the hinge positions of the base, the boom, and the forearm.

[0013] The hydraulic power unit is connected to the rigid robotic arm structure and the flexible joint unit through a valve-controlled drive branch and a volume control branch, respectively. The valve-controlled drive branch and the volume control branch share a hydraulic power source. The valve-controlled drive branch regulates the hydraulic flow into the rigid robotic arm structure, and the volume control branch regulates the fluid injection and recovery into the flexible joint unit. Pressure sensors are installed in both the valve-controlled drive branch and the volume control branch.

[0014] II. A collaborative control method for a hydraulically driven rigid-flexible coupled robotic arm, comprising: The rigid-flexible coupled robotic arm is controlled by a distributed real-time control system, which includes a host computer and a lower-level real-time controller. The lower-level real-time controller collects pressure sensor signals transmitted by pressure sensors in real time to obtain pressure feedback from the forearm hydraulic cylinder, upper arm hydraulic cylinder, shoulder hydraulic cylinder, and each hydraulic drive cavity. It also collects angle encoder signals transmitted by angle encoders in real time to obtain the pose of each joint in the rigid robotic arm structure, and transmits this as the system status to the host computer. Simultaneously, the position of each motion capture calibration ball in the flexible joint unit is obtained through a motion capture system camera to determine the actual pose of the end effector of the flexible joint unit. The signal is then transmitted to the host computer. Based on the target pose of the end effector of the flexible joint unit of the rigid-flexible coupling robotic arm, the host computer sends control signals to the lower-level real-time controller. The lower-level real-time controller outputs valve control commands and volume control commands to the valve control drive branch and volume control branch of the hydraulic power unit, respectively. First, it controls the hydraulic cylinders of the forearm, upper arm, and shoulder of the rigid robotic arm structure in real time to move the flexible joint unit to the vicinity of the target working area to complete macroscopic positioning. Then, it controls the pressure of each hydraulic drive chamber of the flexible joint unit in real time to perform fine-tuning of the posture, so that the end effector of the flexible joint unit moves to the target pose to perform the operation.

[0015] The flexible joint unit employs single-branch independent drive, multi-branch differential drive, and multi-branch synchronous drive modes. In the single-branch independent drive mode, working medium is injected into a single hydraulic drive cavity, causing the flexible joint unit to deflect within a single bending plane. In the multi-branch differential drive mode, working medium is injected differentially into multiple adjacent hydraulic drive cavities, causing the flexible joint unit to bend in the composite direction. In the multi-branch synchronous drive mode, approximately equal amounts of working medium are injected into multiple hydraulic drive cavities simultaneously, causing the flexible joint unit to undergo axial elongation or compliant adjustment while maintaining an approximately straight posture. Each branch corresponds to one hydraulic drive cavity.

[0016] The rigid hydraulic robotic arm structure of this invention is equipped with hydraulic cylinders at each joint. The cylinder body end and piston rod end of the hydraulic cylinder are rotatably connected to adjacent rigid connecting rods on both sides of the corresponding joint via pins, so as to convert the extension and retraction motion of the hydraulic cylinder into the rotation of the adjacent rigid connecting rods around the joint axis. The end of the hydraulic drive cavity of the flexible joint unit is fixed by a clamp, and the top connector is provided with a quick connector that communicates with the hydraulic drive cavity. Through the synergistic effect of the retractable constraint layer, the limiting structure and the axial preload return component, a stable and identifiable correspondence is formed between the volume input and bending output of the hydraulic drive cavity, and the return-to-center capability and repeatability consistency after unloading are improved. During operation, the rigid hydraulic robotic arm is first controlled to complete macroscopic positioning. Then, based on the volume-pressure-attitude recognition model of the flexible joint unit, the end-effector pose compensation is converted into the target volume increment of each hydraulic drive chamber's corresponding branch. The model feedforward term and the proportional-integral-derivative PID feedback term are superimposed to coordinate the control of the servo pump and high-speed solenoid valve. The control system can select a single-branch independent drive, a dual-branch differential drive, or a three-branch synchronous drive mode according to the target attitude to respectively achieve deflection in the corresponding bending plane, bending in the synthetic direction, and compliant adjustment under axial elongation or near-linear attitudes. This invention combines high-load macroscopic operation capability, compliant operation capability in confined spaces, and high end-effector positioning accuracy, making it suitable for precision operations in underwater exploration, deep-sea sampling, and unstructured environments.

[0017] Compared with existing technologies, the improvements of this invention are mainly reflected in the following three aspects: First, the flexible structure is improved by using the coordinated design of the hydraulic drive cavity, the stretchable constraint layer, the limiting structural components, and the axial preload return components to limit radial expansion and provide stable axial return force, making the volume input and bending output relationship of the flexible joint unit more stable and easier to identify; Second, the coordinated control is improved by integrating the installation geometry of the hydraulic cylinders of each joint of the rigid robotic arm with the volume-pressure-attitude identification model of the flexible joint unit into the control link, and combining model feedforward and PID feedback to achieve hierarchical coordination of macro-positioning and end-effector fine-tuning; Third, the system design is improved by using lightweight connectors, unified hydraulic power supply, and integrated layout oriented towards pipelines and sensor feedback to improve the assemblability, wiring reliability, and engineering application adaptability of the whole machine.

[0018] The beneficial effects of this invention are: 1. Performance integration for complex underwater operations: By integrating a high-load rigid hydraulic manipulator with a parallel flexible end joint unit into the same working platform, a unified macroscopic positioning capability and a compliant micro-operation capability in confined spaces are achieved, avoiding the shortcomings of relying solely on a single rigid or flexible actuator, which makes it difficult to balance load, accuracy and safety.

[0019] 2. Clear rigid joint drive relationship: The shoulder hydraulic cylinder, upper arm hydraulic cylinder and lower arm hydraulic cylinder are respectively arranged between adjacent rigid connecting rods on both sides of the corresponding joint, and are connected by pins to form a calculable cylinder stroke-joint angle geometric relationship, which facilitates drive stroke matching, assembly calibration and macro-positioning control.

[0020] 3. Improved Flexible Structure and Its Advantages: The hydraulically driven cavity, the expandable constraint layer, the limiting structural components, and the axial pre-tightening return components work together to effectively improve the correspondence stability between volume input and attitude output by limiting radial expansion, constraining the relative movement of parallel branches, and providing restoring force in the central axis direction. This gives the flexible joint unit higher repeatability, better unloading and centering capability, and better motion controllability.

[0021] 4. Advantages of improved collaborative control: By integrating the geometric relationship between the cylinder stroke and joint angle of the rigid joint hydraulic cylinder and the volume-pressure-attitude parameter identification model of the flexible joint unit into the control link, and adopting a composite control method that combines model feedforward and PID feedback, the desired end attitude compensation can be directly converted into quantitative volume adjustment commands for the corresponding branches of each hydraulic drive cavity. This significantly improves the collaborative accuracy between macro positioning and end fine adjustment, the bending angle control accuracy, and the end trajectory tracking accuracy.

[0022] 5. Unified hydraulic power supply and safety control: The rigid robotic arm and flexible joint unit share the hydraulic power source and a multi-source sensor feedback network, which reduces the complexity of the system interface and enables end-effector contact monitoring, overload protection and compliant gripping control through cavity pressure feedback, thereby improving the overall engineering applicability and underwater operation reliability.

[0023] 6. Compact and easy-to-wire connection transition structure: The connector adopts a lightweight transition arrangement, which provides continuous passage space for hydraulic lines, sensor lines and end tool lines while meeting the rigidity of the rigid-flexible connection. This reduces the additional load at the end, reduces the risk of exposed and tangled pipelines, and improves the convenience of assembly and maintenance. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the rigid-flexible coupling robotic arm of the present invention; Figure 2 This is a schematic diagram of the rigid robotic arm structure and its joint hydraulic cylinder arrangement according to the present invention; Figure 3 This is a schematic diagram of the overall structure of the flexible joint unit of the present invention; Figure 4 This is a schematic diagram showing the arrangement of the axial preload recovery member on the flexible joint unit of the present invention; Figure 5 This is a schematic diagram of the top connector of the present invention; Figure 6 This is a schematic diagram of the bottom connector of the present invention; Figure 7 This is a schematic diagram of the structure of the fixing bracket of the present invention; Figure 8 This is a schematic diagram of the connection structure between the rigid robotic arm structure and the flexible joint unit of the present invention. Figure 9 This is a diagram of the hydraulic drive and collaborative control architecture of the rigid-flexible coupling robotic arm of the present invention. Figure 10 This is a schematic diagram of an experimental scenario for obtaining the end-effector pose feedback of the flexible joint unit of the present invention. Figure 11 This is a schematic diagram of the underwater precision operation of the rigid-flexible coupling robotic arm of the present invention; In the diagram: 100. Rigid robotic arm structure; 101. Base; 102. Shoulder; 103. Upper arm; 104. Forearm; 111. Shoulder joint; 112. Upper arm joint; 113. Forearm joint; 121. Forearm hydraulic cylinder; 122. Upper arm hydraulic cylinder; 123. Shoulder hydraulic cylinder; 1041. Forearm end through hole; 200. Flexible joint unit; 201. Top connector; 202. Bottom connector; 203. Limiting structure; 204. Extendable constraint layer; 205. Clamp. 206. Hydraulic drive cavity; 207. Axial preload return component; 2011. Top connector through hole; 2021. Bottom connector through hole; 211. Dynamic capture calibration ball; 212. Bolt; 213. Fixed bracket; 214. Quick connector; 2131. First calibration ball connection through hole; 2132. Through hole; 2133. Flexible arm connection through hole; 2134. Second calibration ball connection through hole; 300. Connector; 301. Forearm connection through hole; 302. Fixed bracket connection through hole. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1As shown, the hydraulically driven rigid-flexible coupling robotic arm of the present invention includes a rigid robotic arm structure 100, a flexible joint unit 200 equipped with an axial preload return member 207 and a dynamic capture calibration ball 211, a connector 300, and a hydraulic power unit. The root end of the rigid robotic arm structure 100 is installed at a fixed position, and the root end of the flexible joint unit 200 is installed at the end of the rigid robotic arm structure 100 through the connector 300. An end effector, such as a flexible gripper or sampling tool, is installed at the end of the flexible joint unit 200, and a camera is also installed thereon, enabling the robotic arm to complete continuous operations such as target approach, attitude adjustment, compliant grasping, and sampling detection on the same platform. The hydraulic power unit is connected to the rigid robotic arm structure 100. The rigid robotic arm structure 100 and flexible joint unit 200 provide a hydraulic power source. The rigid robotic arm structure 100 performs macroscopic positioning near the underwater target area and provides the overall robotic arm with a large working space, high load capacity, and stable base posture. The flexible joint unit 200 performs fine end-effector adjustment through axial preload return member 207 and dynamic capture calibration ball 211 to perform integrated operation on the underwater target through the end effector. The flexible joint unit 200 is used to complete fine end-effector attitude adjustment, compliant contact, and fine operation in confined spaces. When the end effector is a flexible gripper, the drive circuit of the flexible gripper is connected in parallel to the volume control branch of the hydraulic power unit for independent control.

[0027] like Figure 2 and Figure 3As shown, the rigid robotic arm structure 100 includes a base 101, a large arm 103, a small arm 104, a small arm hydraulic cylinder 121, a large arm hydraulic cylinder 122, and a shoulder hydraulic cylinder 123. The base 101 is installed in a fixed position. The base 101, the large arm 103, and the small arm 104 are connected in series and hinged together. The base 101 and the large arm 103 are hinged together by a connecting bracket. One end of the connecting bracket is hinged to the end of the base 101. The cylinder body of the shoulder hydraulic cylinder 123... Located in the base 101, with its root end synchronously connected to one end of the connecting bracket and the hinge position of the base 101 via a pin, the connecting bracket rotates about the vertical joint axis of the shoulder joint 111 of the shoulder 102 at its hinge position with the base 101; the other end of the connecting bracket is synchronously connected to the root end of the boom 103 via a hinged connecting rod, and the cylinder body of the boom hydraulic cylinder 122 is located in the boom 103, with its root end hinged to the boom 103 via a pin. The boom hydraulic cylinder 122's end piston rod is synchronously connected to the hinge position of the connecting bracket and the connecting rod via a pin, allowing the boom 103 to rotate around the horizontal joint axis of the boom joint 112 at the hinge position of the connecting bracket and the connecting rod. The forearm hydraulic cylinder 121's cylinder body is located in the boom 103, and its root end is hinged to the middle of the boom 103 via a pin. The end piston rod of the forearm hydraulic cylinder 121 is synchronously connected to the hinge position of the boom 103 and the forearm 104 via a pin, allowing the forearm 104 to rotate around the horizontal joint axis of the forearm joint 113 at its hinge position with the boom 103. The end of the forearm 104 and its through hole 1041 are connected by a connector 300 to install a flexible joint unit 200. The forearm hydraulic cylinder 121, the boom hydraulic cylinder 122, and the shoulder hydraulic cylinder 123 are connected. Angle encoders are installed at the hinge positions of the base 101, the boom 103, and the forearm 104.

[0028] The rigid robotic arm structure 100 comprises a shoulder joint 111, a large arm joint 112, and a forearm joint 113. The rigid robotic arm structure 100 is composed of three rigid links and three rigid joints connected in series. Its power source is a valve-controlled drive circuit. Each rigid joint is equipped with a hydraulic cylinder: a shoulder hydraulic cylinder 123 for driving the shoulder joint 111, a large arm hydraulic cylinder 122 for driving the large arm joint 112, and a forearm hydraulic cylinder 121 for driving the forearm joint 113. The forearm 104 has a forearm end through-hole 1041 for assembly with the connecting member 300. The rigid robotic arm structure 100 is mainly used to achieve large-range macroscopic positioning and attitude adjustment during operations, and provides a stable base for the flexible joint unit 200 after reaching the target area. In the rigid robotic arm structure 100, the cylinder body end of the hydraulic cylinder at each joint is rotatably connected to the front rigid connecting rod on one side of the corresponding joint axis via a pin, and the piston rod end is rotatably connected to the rear rigid connecting rod on the other side of the corresponding joint axis via a pin, so as to form a drive transmission relationship that converts the extension and retraction of the hydraulic cylinder into the joint rotation angle.

[0029] The hydraulic power unit is connected to the rigid robotic arm structure 100 and the flexible joint unit 200 through a valve-controlled drive branch and a volume control branch, respectively. The valve-controlled drive branch and the volume control branch share the same hydraulic power source and use the same hydraulic working medium to reduce system integration complexity and reduce coordination control errors caused by interface differences. The valve-controlled drive branch regulates the hydraulic flow entering the rigid robotic arm structure 100, and the volume control branch regulates the fluid injection and recovery volume entering the flexible joint unit 200. Pressure sensors are installed in both the valve-controlled drive branch and the volume control branch.

[0030] The valve-controlled drive branch includes a motor, a hydraulic pump, and an electro-hydraulic proportional servo valve assembly. The electro-hydraulic proportional servo valve assembly is used to regulate the hydraulic flow entering each joint hydraulic cylinder to control the extension and retraction of the hydraulic cylinders, and to convert the cylinder stroke into joint angle based on the installation geometry of the hydraulic cylinders. The volume control branch includes a servo pump, a high-speed solenoid valve assembly, and inlet and outlet fluid circuits corresponding to each hydraulic drive chamber 206. It is used to quantitatively regulate the fluid injection and recovery volume of each hydraulic drive chamber 206 by coordinating the servo pump speed and the switching timing of the high-speed solenoid valves. In this embodiment, the AC motor and gear pump of the valve-controlled drive branch are preferably coaxially connected and fixedly installed on the hydraulic power unit base via a coupling. The AC motor drives the gear pump to provide high-pressure hydraulic oil to the system. The system working pressure is approximately 16 MPa. The oil outlet of the gear pump is connected to the oil inlet of the electro-hydraulic proportional servo valve assembly through a high-pressure pipeline or an integrated valve block. Each output port of the electro-hydraulic proportional servo valve assembly is connected to each joint hydraulic cylinder of the rigid robotic arm structure 100 via pipelines. The servo pump and high-speed solenoid valve assembly are preferably mounted on a volume control valve block or mounting bracket. Each branch is connected to the quick connector 214 on the top connector 201 of the flexible joint unit 200 via a high-pressure hose. The cylinder ends of the shoulder hydraulic cylinder 123, upper arm hydraulic cylinder 122, and lower arm hydraulic cylinder 121 are rotatably connected to the front rigid connecting rod on one side of the corresponding joint axis via pins, and the piston rod ends are rotatably connected to the rear rigid connecting rod on the other side of the corresponding joint axis via pins, so that each hydraulic cylinder and the adjacent rigid connecting rod form a driving force transmission geometric relationship. When each hydraulic cylinder extends or retracts, the distance between the two connection points changes, thereby driving the adjacent rigid connecting rod to rotate around the corresponding joint axis to achieve posture adjustment of the shoulder joint 111, upper arm joint 112, and lower arm joint 113. By adjusting the flow rate into each hydraulic cylinder through an electro-hydraulic proportional valve, the joint motion control of the three degrees of freedom of the rigid robotic arm structure 100 can be achieved.

[0031] Pressure sensors are installed in the valve control branch of the rigid robotic arm structure 100 and the volume control branch of the flexible joint unit 200, respectively. Specifically, the pressure sensors corresponding to the shoulder hydraulic cylinder 123, the upper arm hydraulic cylinder 122, and the lower arm hydraulic cylinder 121 are preferably installed between the corresponding valve port of the electro-hydraulic proportional servo valve group and the hydraulic cylinder port, and close to the side of the hydraulic cylinder; the pressure sensors corresponding to each hydraulic drive cavity 206 of the flexible joint unit 200 are preferably installed on the branch pipeline between the high-speed solenoid valve group and the quick connector 214 of the top connector 201, for measuring the working pressure of the rigid joint hydraulic cylinder and the pressure inside each hydraulic drive cavity 206. The electrical signal output terminal of each pressure sensor is electrically connected to the analog input module. Since the sensor mounting point is close to the actuator, the measured pressure can approximately reflect the real-time pressure state of the corresponding actuator and is used for force control feedback, contact judgment, and overload protection.

[0032] In a preferred embodiment, the mounting point position, joint axis position and initial length of each joint hydraulic cylinder of the rigid robotic arm structure 100 are calibrated during the assembly stage. The distributed real-time control system establishes a geometric mapping relationship between the hydraulic cylinder extension and joint rotation angle based on preset installation geometric parameters, and completes the target joint angle calculation, valve opening conversion and macroscopic positioning closed-loop control of the rigid robotic arm accordingly.

[0033] like Figure 4 and Figure 5As shown, the flexible joint unit 200 also includes a top connector 201, a bottom connector 202, several hydraulically driven flexible components installed between the top connector 201 and the bottom connector 202, several limiting structural components 203, and two fixed supports 213. The top connector 201 and the bottom connector 202 are arranged parallel and spaced apart when the flexible joint unit 200 is in a straight state. Each hydraulically driven flexible component is evenly spaced circumferentially and its two ends are respectively connected to the opposite side of the top connector 201 and the bottom connector 202. There are at least three hydraulically driven flexible components. Each limiting structural component 203 is evenly spaced axially along the flexible joint unit 200 and is not connected to the top connector 201 and the bottom connector 202. The axial pre-tightening return components 207 are spaced at the center of each hydraulically driven flexible component and their two ends are respectively connected to the center of the opposite side of the top connector 201 and the bottom connector 202, forming a... A helical guide fixing pair for axial positioning and anti-detachment fixation, with an axial pre-tightening return member 207 arranged along the central axis of the flexible joint unit 200; two fixing brackets 213 are respectively fitted onto the outer periphery of the top connector 201 and the bottom connector 202 through the top connector through hole 2011, the bottom connector through hole 2021 and the through hole 2132; every two motion capture calibration balls 211 form a ball group; several ball groups are evenly spaced around each fixing bracket 213; the two motion capture calibration balls 211 in each ball group are respectively installed on the side of the fixing bracket 213 near and away from the flexible joint unit 200 through bolts 212, the first calibration ball connecting through hole 2131 and the second calibration ball connecting through hole 2134; the top connector 201 is installed at the end of the rigid robotic arm structure 100 through the flexible arm connecting through hole 2133 and the forearm connecting through hole 301 of the connector 300 and the fixing bracket connecting through hole 302.

[0034] like Figure 7 and Figure 8As shown, the fixed bracket 213 is provided with flexible arm connection through holes 2133 and 2132, and calibration ball connection through holes 2131 and 2134. The top connector through hole 2011 and the bottom connector through hole 2021 can be connected to the flexible arm connection through hole 2133 on the fixed bracket 213 by bolts 212 or pins; in heavy-load operation scenarios, bolt connection is preferred, while in light-load operation scenarios, pin connection that meets the interference fit requirements can also be used. The connector 300 is provided with a forearm connection through hole 301 that mates with the through hole 1041 at the end of the rigid robotic arm structure 100 and a fixed bracket connection through hole 302 that mates with the fixed bracket 213. The rigid robotic arm structure 100 and the flexible joint unit 200 are reliably assembled by bolt connection; when quick assembly and disassembly are required, a pin and limit fit structure can also be used. The connector 300 preferably adopts a plate-frame transition connection structure. While ensuring the end-effector rigidity and assembly accuracy of the rigid robotic arm structure 100, it forms a clearance area and a weight-reduction area in the middle to reduce the added mass and rotational inertia at the end, thus mitigating the impact on the end-effector load of the rigid robotic arm structure 100. Specifically, the top connector 201 has three evenly spaced ball groups mounted on its fixed bracket 213, and the bottom connector 202 has four evenly spaced ball groups mounted on its fixed bracket 213. The first calibration ball connection through holes 2131 are distributed along a circular equilateral triangle, and the second calibration ball connection through holes 2134 are distributed along a circular square.

[0035] A motion capture calibration ball 211 is detachably mounted on the fixed bracket 213, facilitating the pose calibration and experimental verification of the flexible joint unit 200. Multiple motion capture calibration balls 211 can be respectively installed at the calibration ball connection through-holes 2131 distributed along the circumference in an equilateral triangle and at the calibration ball connection through-holes 2134 distributed along the circumference in a square. This helps to distinguish the spatial orientation of the flexible joint unit 200 in the optical motion capture system and reduces the impact of bracket obstruction on pose measurement. The fixed bracket 213 and motion capture calibration balls 211 are preferably used in the laboratory parameter identification, control verification, and prototype debugging stages. In the actual underwater operation stage, the motion capture calibration balls 211 and multiple motion capture cameras are not essential; the end-effector pose feedback of the flexible joint unit 200 can be provided by an underwater visual measurement system, an underwater positioning measurement system, or pre-calibrated operational coordinates. Target object pose information can be provided by pre-input operational point coordinates, teaching trajectories, or external sensing systems. This invention does not limit the acquisition of the target object position to a motion capture system. Figure 10 As shown, the identification of the motion capture calibration ball 211 and the acquisition of the end pose of the flexible joint unit 200 are demonstrated in the experimental scenario. Furthermore, when the fixed bracket 213 is connected to the bottom connector 202, its through hole 2132 can be used to expand the end-effector connection space, such as by installing flexible grippers, cameras, samplers, or other end-effector tools through intermediate adapter structures, to adapt to different underwater operation tasks.

[0036] The flexible joint unit 200 is connected to the end of the rigid robotic arm structure 100. Internally, it includes three independent hydraulic drive cavities 206, arranged in an equilateral triangle along the circumference between the top connector 201 and the bottom connector 202. Each hydraulic drive cavity 206 is covered by a stretchable constraint layer 204 and constrained by axially spaced limiting structures 203. An axial preload return member 207 is positioned along the central axis of the flexible joint unit 200 to provide axial preload force and return force after unloading. The three hydraulic drive cavities 206 can achieve two-dimensional bending and slight axial expansion / contraction of the flexible joint unit through single-branch independent drive, dual-branch differential drive, or three-branch synchronous drive. The hydraulic drive cavities 206 can be made of Dragon Skin 30 or a similar elastic material to provide good compliance and sealing.

[0037] Both the top connector 201 and the bottom connector 202 have a spiral groove at their center on one side facing each other. The spiral groove extends continuously along the circumference and does not extend beyond the other side of the top connector 201 and the bottom connector 202. The axial preload return member 207 is a helical spring arranged along the central axis of the flexible joint unit 200. Both ends of the axial preload return member 207 are spirally connected to the spiral groove. The end of the axial preload return member 207 is screwed into the spiral groove to provide axial preload force and unloading return force for unilateral drive of the flexible joint unit 200, while reducing residual deformation and improving repeatability. The joint between the axial preload return member 207 and the spiral groove is also filled with a sealing adhesive material to improve the anti-loosening performance, sealing performance and long-term service stability of the end connection.

[0038] like Figure 6 and Figure 7As shown, the top connector 201 has several connecting bosses with central through holes evenly spaced along the circumference on one side facing the bottom connector 202. Each connecting boss has a threaded hole on the other side of the top connector 201, coaxial with and connected to the through hole of its respective connecting boss. A quick-connect plug 214 connects to each threaded hole, thus connecting to the hydraulic power unit. The bottom connector 202 has several connecting bosses evenly spaced along the circumference on one side facing the top connector 201, each coaxial with its respective connecting boss. Each hydraulically driven flexible component includes a retractable constraint layer 204, two clamps 205, and a hydraulic drive cavity 206. The retractable constraint layer 204 is specifically a bellows, and the hydraulic drive cavity 206 is preferably a hollow column of flexible material. The structure consists of a retractable constraint layer 204 coaxially fitted over the outside of the hydraulic drive cavity 206. The two ends of the hydraulic drive cavity 206 are respectively fitted onto the connecting bosses of the top connector 201 and the bottom connector 202, thus connecting to the quick connector 214. Two clamps 205 are respectively fitted onto the outer circumference of both ends of the retractable constraint layer 204, thereby clamping the retractable constraint layer 204 and the two ends of the hydraulic drive cavity 206 together onto the connecting bosses, achieving mechanical fixation and fluid sealing. In specific implementation, there are three retractable constraint layers 204, arranged in an equilateral triangle between the top connector 201 and the bottom connector 202. The axial pre-tightening return element 207 is located at the center of the three retractable constraint layers 204.

[0039] The bottom connector 202 has a number of connecting bosses equal to the number of hydraulic drive cavities 206 and bottom connector through holes 2021. The connecting bosses are evenly spaced along the circumference to ensure the symmetry of the parallel branches and the balanced force on the flexible joint unit 200. The top connector 201 has corresponding top connector through holes 2011 and quick connectors 214; the quick connectors 214 are connected to the hydraulic drive cavities 206 to enable communication between the working medium and each hydraulic drive cavity 206. The hydraulic drive cavity 206 is preferably a hollow cylindrical tubular structure, with its two ends respectively fitted onto the connecting bosses of the top connector 201 and the bottom connector 202 to form sealed cavities. The working medium communicates with the external hydraulic circuit through the quick connectors 214 on the top connector 201.

[0040] The limiting structure 203 is sheet-shaped, and each limiting structure 203 has a circumferential limiting hole and a central limiting hole for passing through each expandable constraint layer 204 and the axial pre-tightening return member 207. Each limiting structure 203 is evenly spaced and fitted onto each expandable constraint layer 204 and the axial pre-tightening return member 207 to limit the radial expansion of the expandable constraint layer 204 and the relative radial displacement between adjacent expandable constraint layers 204, so that the fluid volume change is preferentially converted into axial expansion and bending deformation. When the flexible joint unit 200 is in a straight state, the limiting structure 203 is parallel to the top connector 201 and the bottom connector 202, and each limiting structure 203 is located between the clamps 205 at both ends.

[0041] The limiting structure 203 is preferably made of an elastic material such as TPU and is spaced axially on the outside of the hydraulic drive cavity 206; in a preferred embodiment, the center-to-center distance between adjacent limiting structure 203 is 2 mm. The limiting structure 203 can effectively limit the radial expansion of the hydraulic drive cavity 206 while maintaining overall compliance, thereby improving the motion consistency and control accuracy of the flexible joint unit 200.

[0042] The design principle of the flexible joint unit 200 is that the hydraulic drive cavity 206 is constrained on the periphery by the stretchable constraint layer 204, and the relative displacement of each parallel branch is restricted by the axially distributed limiting structure 203. At the same time, the axial pre-tightening and recovery component 207 provides pre-tightening force and centering recovery force in the central axis direction, so that the change in liquid volume is preferentially converted into axial length change and overall bending deformation, thereby reducing radial bulging, hysteresis and residual deformation, and improving the consistency of repeated positioning, unloading recovery capability and parameter identification stability.

[0043] The collaborative control method for the hydraulically driven rigid-flexible coupled robotic arm of the present invention is as follows: The rigid-flexible coupling robotic arm is controlled by a distributed real-time control system, which includes a host computer (LabVIEW) and a lower-level real-time controller. The lower-level controller acquires pressure sensor signals transmitted from pressure sensors in real time to obtain pressure feedback from the forearm hydraulic cylinder 121, the upper arm hydraulic cylinder 122, the shoulder hydraulic cylinder 123, and each hydraulic drive cavity 206. It also acquires angle encoder signals transmitted from the angle encoder to obtain the joint poses of the rigid robotic arm structure 100, which are then transmitted to the host computer as system status. Simultaneously, the position of each motion capture calibration ball 211 in the flexible joint unit 200 is acquired through the motion capture system camera to determine the actual pose of the end effector of the flexible joint unit 200, which is then transmitted to the host computer via TCP / IP protocol. The host computer sends control signals to the lower-level real-time controller based on the target pose of the end effector of the flexible joint unit 200 of the rigid-flexible coupling robotic arm, and the lower-level real-time controller outputs valve control commands accordingly. In the specific implementation, the target volume increment of each hydraulic drive cavity corresponding to the flexible joint unit 200 is calculated based on the target posture compensation amount of the flexible joint unit 200. The feedforward control quantity is generated based on the target volume increment, and the feedforward control quantity is superimposed with the PID feedback control quantity based on the posture error to obtain the volume control command. The servo pump and high-speed solenoid valve are coordinated and controlled according to the volume control command, thereby improving the trajectory tracking accuracy, posture holding accuracy and repeatability accuracy of the flexible joint unit 200. First, the forearm hydraulic cylinder 121, upper arm hydraulic cylinder 122 and shoulder hydraulic cylinder 123 of the rigid robotic arm structure 100 are controlled in real time to move the flexible joint unit 200 to the vicinity of the target working area to complete the macro positioning. Then, the pressure of each hydraulic drive cavity 206 of the flexible joint unit 200 is controlled in real time to perform posture fine adjustment, so that the end of the flexible joint unit 200 moves to the target posture to perform the operation.

[0044] At the control level, before performing attitude fine-tuning, the flexible joint unit 200 is first zero-position calibrated and parameter identified using each motion capture calibration ball 211. This yields the volume-equivalent length conversion parameters, pressure compensation parameters, and leakage compensation parameters for each hydraulic drive chamber 206 corresponding branch. During operation, the end effector target pose is decomposed into macroscopic valve control commands from the rigid robotic arm structure 100 and fine-tuning volume control commands from the flexible joint unit 200. Based on the parameter identification results, a volume-pressure-attitude mapping relationship is established, and the feedforward control quantity for each hydraulic drive chamber 206 corresponding branch is calculated accordingly. After the rigid robotic arm structure 100 completes macroscopic positioning, the target volume increment for each hydraulic drive chamber 206 corresponding branch is calculated based on the volume-pressure-attitude mapping relationship of the flexible joint unit 200. The volume control branch is coordinated to quantitatively inject and return fluid to each hydraulic drive chamber 206, achieving precise positioning and compliant operation of the end effector.

[0045] The host computer is responsible for human-computer interaction, task planning, and status monitoring, while the lower-level real-time controller is responsible for real-time data acquisition and synchronously outputting valve control commands for the rigid robotic arm structure 100 and volume control commands for the flexible joint unit 200. The lower-level real-time controller is connected to the analog output module NI-9264, the analog input module NI-9220, and the bus communication module (CANopen) NI-9881. The analog output module is used to output valve control commands for the rigid robotic arm and volume control commands for the flexible joint unit. The analog input module is connected to the system pressure sensor, and the bus communication module is connected to the absolute encoders at each joint of the rigid robotic arm.

[0046] The distributed real-time control system of this invention adopts a hierarchical architecture of host computer and real-time controller, and communicates commands and status via TCP / IP protocol to achieve coordinated motion control of the rigid robotic arm structure 100 and the flexible joint unit 200. The real-time controller preferably uses a real-time controller built on the NI cRIO platform, along with its analog input module, analog output module, and bus communication module plugged into the backplane of its chassis, which together constitute the system's data acquisition and control output unit. The real-time controller is electrically connected to each module via the backplane bus and forms the closed-loop control core of the system, used to perform rigid robotic arm position control, flexible joint unit parameter identification, feedforward-feedback composite control, pressure threshold monitoring, and multi-source sensor information fusion. The host computer preferably uses a LabVIEW software environment highly compatible with the hardware platform, sending trajectory planning commands and task switching commands via TCP / IP protocol and performing system status monitoring.

[0047] In this embodiment, the NI9220 analog input module is selected. This module has 16 analog input channels, 16-bit resolution, and a sampling rate of up to 200 kS / s, capable of acquiring ±10V voltage signals, matching the output range of the pressure sensors and flow measurement unit. The input terminals of the analog input module are electrically connected to each pressure sensor and other analog sensors for real-time acquisition of signals such as the working pressure of the rigid joint hydraulic cylinder, the pressure of each branch cavity of the flexible joint unit, flow rate, and contact status.

[0048] The analog output module uses the NI-9264 D / A module to output high-precision analog voltage signals. The output terminals of the analog output module are electrically connected to the electro-hydraulic proportional servo valve driver, the servo pump driver in the volume control branch, and the high-speed solenoid valve drive circuit of the rigid robotic arm structure 100, respectively. Its output signals are used to adjust the valve opening of the corresponding valves of the hydraulic cylinders of each joint, and to output the pump speed command and valve control command of the volume control branch of the flexible joint unit 200, so as to achieve precise adjustment of the injection and return volumes of each hydraulic drive chamber 206.

[0049] The bus communication module, for example, uses a module supporting the CANopen protocol. One end of the module is connected to the real-time controller via a backplane, and the other end is connected to the absolute encoders installed at each joint of the rigid robotic arm structure 100 via an industrial fieldbus for real-time reading of joint position information. Angle encoders are preferably installed at the joint shafts of the shoulder joint 111, upper arm joint 112, and forearm joint 113, or at the end of a drive shaft coaxially connected to the joint shafts, for outputting angle feedback for each joint.

[0050] It also includes a multi-source sensor feedback network, which includes at least the joint angle feedback of the rigid robotic arm structure 100, the end-effector pose feedback of the flexible joint unit 200, and the internal pressure feedback of each hydraulic drive cavity 206. The end-effector pose feedback of the flexible joint unit 200 is provided by an external pose measurement system, which includes at least one of an optical motion capture system, a vision measurement system, or an underwater positioning measurement system, for attitude closed-loop control and end-effector contact safety monitoring of the flexible joint unit 200.

[0051] The flexible joint unit 200 adopts single-branch independent drive, multi-branch differential drive, and multi-branch synchronous drive modes. In the single-branch independent drive mode, working medium is injected into a single hydraulic drive cavity 206, and the flexible joint unit 200 deflects in a single bending plane. In the multi-branch differential drive mode, working medium is injected differentially into multiple adjacent hydraulic drive cavities 206, and the flexible joint unit 200 forms a composite bending direction. In the multi-branch synchronous drive mode, approximately equal amounts of working medium are injected into multiple hydraulic drive cavities 206 simultaneously, and the flexible joint unit 200 produces axial elongation or compliant adjustment while maintaining an approximately straight posture. Each branch corresponds to one hydraulic drive cavity 206.

[0052] When the flexible joint unit 200 is composed of three hydraulic drive chambers 206, the bending angle and bending plane angle of the flexible joint unit 200 are calculated based on the equivalent length of the corresponding branch of each hydraulic drive chamber 206. The single-branch independent drive, dual-branch differential drive, or three-branch synchronous drive mode is selected according to the target bending direction, bending amplitude, and axial elongation of the flexible joint unit. In the control process, the pressure feedback and the safety threshold are compared in real time. When the pressure feedback reaches the preset threshold, the volume control command is reduced or the injection is stopped to achieve overload protection and compliant contact control.

[0053] The design principle of collaborative control is to first use the geometric driving relationship of the hydraulic cylinders of each joint of the rigid hydraulic manipulator structure 100 to complete the large-scale macro positioning, and then use the parameter identification model of the flexible joint unit 200 to decompose the end-effector small-scale pose compensation amount into the volume adjustment amount of each hydraulic drive cavity 206 corresponding branch. The nonlinearity of the branch is compensated by model feedforward, and external disturbances and modeling errors are suppressed by PID feedback, thereby improving the end-effector positioning accuracy and compliant contact stability.

[0054] The volume control branch of the valve-controlled drive circuit is a pump-valve coordinated volume control system, the core of which includes a servo pump, a high-speed solenoid valve array, and inlet / outlet fluid circuits corresponding to the three hydraulic drive chambers 206. The distributed real-time controller precisely regulates the fluid volume injected into or extracted from each hydraulic drive chamber 206 by coordinating the rotational speed of the servo pump and the on / off timing and duty cycle of each solenoid valve, thereby driving the flexible joint unit 200 to generate the target bending posture. In this embodiment, the volume control branch is equipped with four independent control loops, three of which correspond to the three hydraulic drive chambers 206 respectively, and the other control loop is used to drive the flexible gripper; each control loop can independently complete quantitative fluid injection, pressure holding, and active fluid return according to control commands, to balance posture adjustment and end-effector grasping.

[0055] During the specific driving process, when only a single hydraulic drive chamber 206 is injected while the remaining hydraulic drive chambers are pressure-maintained or refluided, the flexible joint unit 200 deflects in the bending plane corresponding to that drive branch. When two adjacent hydraulic drive chambers 206 are injected simultaneously with a difference in injection volume, the flexible joint unit 200 bends in the composite direction. When three hydraulic drive chambers 206 are injected with approximately equal amounts of working medium simultaneously, the flexible joint unit 200 primarily elongates axially and can achieve compliant contact adjustment while maintaining an approximately straight posture. The axial preload recovery component 207 provides a centering restoring force to the flexible joint unit 200 during the above process, making it easier to return to its initial posture after unloading, and helping to reduce residual deformation and improve repeatability. All of the above different driving modes can be achieved by the same volume control branch by switching the on / off sequence of the high-speed solenoid valve and the servo pump speed.

[0056] Based on the above system structure, the rigid-flexible coupling robotic arm in this embodiment performs its tasks as follows: First, after the system assembly is completed, the flexible joint unit 200 is calibrated at zero position and its parameters are identified. By applying a known volume input to each hydraulic drive cavity 206 and simultaneously recording the cavity pressure, end-effector pose, and drive displacement, the volume-equivalent length conversion parameters, pressure compensation parameters, and leakage compensation parameters of the corresponding branch of each hydraulic drive cavity 206 are obtained. The zero-position calibration and parameter identification can be repeated during initial system assembly, after replacement of the flexible joint unit 200, after pipeline maintenance, or when the working medium / environmental conditions change significantly, to update the control parameters.

[0057] The pose feedback information is the measurement information characterizing the spatial position and attitude of the end effector of the flexible joint unit 200 and / or the target object, including at least one of three-dimensional position coordinates, attitude angles or their equivalent representations; the end effector pose error is the difference between the target end effector pose and the currently measured end effector pose, including position error and attitude error.

[0058] During operation, the control system performs task planning based on the pre-input work point coordinates, teaching trajectory, or target object pose information obtained from an external pose measurement system. First, it drives the valve-controlled branch of the rigid robotic arm structure 100 to adjust the opening of the electro-hydraulic proportional servo valve, causing the rigid hydraulic robotic arm structure 100 to move rapidly to the vicinity of the target work area, while keeping the base of the flexible joint unit 200 within a working range that allows for fine-tuning. In the experimental calibration and control verification phase, an optical motion capture system can preferably be used to identify the motion capture calibration ball 211 on the fixed support 213 to obtain end-effector pose feedback for the flexible joint unit 200. In the actual underwater operation phase, a visual measurement system, an underwater positioning measurement system, or pre-calibrated work coordinates can be used; it is not required to set up a motion capture calibration ball and multiple motion capture cameras.

[0059] After completing the macroscopic positioning, the control system calculates the required attitude compensation amount based on the pose error at the end of the flexible joint unit 200. In a preferred embodiment, the distributed real-time control system calculates the input volume increment and cavity pressure information of the corresponding branch of each hydraulic drive cavity 206 based on the zero-position parameters, volume-equivalent length conversion parameters and pressure compensation parameters obtained by parameter identification, so as to obtain the equivalent length change of each branch. When the flexible joint unit 200 is composed of three parallel branches, the axial elongation, bending angle and bending plane angle of the flexible joint unit can be solved based on the equivalent length change of each branch. Based on the target bending direction, bending amplitude and axial elongation, the system selects the single-branch independent drive, dual-branch differential drive or three-branch synchronous drive mode, and then uses the target volume increment corresponding to the target attitude as the feedforward control quantity.

[0060] Based on this, the control input of each branch of the flexible joint unit 200 is obtained by superimposing the feedforward control quantity and the feedback correction quantity. The feedback correction quantity is generated according to the proportional-integral-derivative control law based on the end-effector pose error, the cumulative error, and the error change trend. The distributed real-time control system coordinates and adjusts the servo pump speed and the on / off timing of each high-speed solenoid valve according to the control input to realize the quantitative injection, pressure holding, or return of fluid to each hydraulic drive chamber 206, so as to drive the flexible joint unit 200 to complete the end-effector attitude fine adjustment.

[0061] Once the end of the flexible joint unit 200 is aligned with the target, the control system drives the corresponding circuit of the flexible gripper to perform an envelope gripping action. Simultaneously, it compares the pressure feedback from each hydraulic drive chamber 206 with a preset safety threshold in real time. When the pressure reaches the preset threshold, it reduces the volume control command or stops injecting fluid to prevent damage to the target. Experiments show that the robotic arm and control method of this invention can achieve stable support of the rigid robotic arm and precise posture adjustment of the flexible joint unit in complex underwater environments, exhibiting high positioning repeatability, environmental adaptability, and operational safety.

[0062] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A hydraulically driven rigid-flexible coupled robotic arm, characterized in that: The device includes a rigid robotic arm structure (100), a flexible joint unit (200) equipped with an axial preload return component (207) and a motion capture calibration ball (211), a connector (300), and a hydraulic power unit. The root end of the rigid robotic arm structure (100) is installed at a fixed position. The root end of the flexible joint unit (200) is installed at the end of the rigid robotic arm structure (100) through the connector (300). An end effector is installed at the end of the flexible joint unit (200). The hydraulic power unit connects the rigid robotic arm structure (100) and the flexible joint unit (200) to provide a hydraulic power source. The rigid robotic arm structure (100) performs macroscopic positioning of the area where the underwater target is located. The flexible joint unit (200) performs fine end adjustment through the axial preload return component (207) and the motion capture calibration ball (211) to perform integrated operation on the underwater target through the end effector.

2. The hydraulically driven rigid-flexible coupling robotic arm according to claim 1, characterized in that: The flexible joint unit (200) further includes a top connector (201), a bottom connector (202), several hydraulically driven flexible components installed between the top connector (201) and the bottom connector (202), several limiting structures (203), and two fixed supports (213). The top connector (201) and the bottom connector (202) are arranged parallel and spaced apart when the flexible joint unit (200) is in a straight state. Each hydraulically driven flexible component is evenly spaced along the circumference and its two ends are respectively connected to the opposite side of the top connector (201) and the bottom connector (202). Each limiting structure (203) is evenly spaced along the axial direction of the flexible joint unit (200). The pre-tightening return piece (207) is spaced at the center of each hydraulically driven flexible component and its two ends are respectively connected to the center of the side opposite to the top connector (201) and the bottom connector (202); two fixed brackets (213) are respectively fitted on the outer periphery of the top connector (201) and the bottom connector (202), each pair of motion capture calibration balls (211) forms a ball group, and several ball groups are evenly spaced in the circumference of each fixed bracket (213). The two motion capture calibration balls (211) in each ball group are respectively installed on the fixed bracket (213) on the side close to and away from the flexible joint unit (200); the top connector (201) is installed at the end of the rigid robotic arm structure (100) through the connector (300).

3. The hydraulically driven rigid-flexible coupling robotic arm according to claim 2, characterized in that: The top connector (201) has three evenly spaced ball groups installed on the fixed bracket (213), and the bottom connector (202) has four evenly spaced ball groups installed on the fixed bracket (213).

4. The hydraulically driven rigid-flexible coupling robotic arm according to claim 2, characterized in that: The top connector (201) and the bottom connector (202) are provided with a spiral groove at the center of their opposite sides. The spiral groove extends continuously along the circumference and does not exceed the other side of the top connector (201) and the bottom connector (202). The axial preload recovery member (207) is a spiral spring arranged along the central axis of the flexible joint unit (200). The two ends of the axial preload recovery member (207) are respectively spirally connected in the spiral groove. The end of the axial preload recovery member (207) is screwed into the spiral groove to provide axial preload force and unloading recovery force for unilateral drive of the flexible joint unit (200), while reducing residual deformation and improving repeatability consistency.

5. The hydraulically driven rigid-flexible coupled robotic arm according to claim 2, characterized in that: The top connector (201) has several connecting bosses with central through holes evenly spaced along the circumference on the side facing the bottom connector (202). Each connecting boss has a threaded hole on the other side of the top connector (201). Each threaded hole is coaxial with and connected to the through hole of its respective connecting boss. A quick-connect plug (214) is connected to each threaded hole, thus connecting to the hydraulic power unit. The bottom connector (202) has several connecting bosses evenly spaced along the circumference on the side facing the top connector (201). Each connecting boss is coaxial with its respective connecting boss. Each hydraulically driven flexible component package... It includes a retractable constraint layer (204), two clamps (205) and a hydraulic drive cavity (206). The retractable constraint layer (204) is coaxially fitted over the outside of the hydraulic drive cavity (206). The two ends of the hydraulic drive cavity (206) are respectively fitted onto the connecting boss of the top connector (201) and the connecting boss of the bottom connector (202) to connect to the quick connector (214). The two clamps (205) are respectively fitted onto the outer circumference of the two ends of the retractable constraint layer (204) to clamp the two ends of the retractable constraint layer (204) and the two ends of the hydraulic drive cavity (206) together onto the connecting boss and the connecting boss.

6. The hydraulically driven rigid-flexible coupled robotic arm according to claim 5, characterized in that: The limiting structure (203) is in the form of a sheet. Each limiting structure (203) has a circumferential limiting hole and a central limiting hole for passing through each stretchable constraint layer (204) and the axial pre-tightening recovery component (207). Each limiting structure (203) is evenly spaced and fitted onto each stretchable constraint layer (204) and the axial pre-tightening recovery component (207) to limit the radial expansion of the stretchable constraint layer (204) and the relative radial displacement between adjacent stretchable constraint layers (204), so that the fluid volume change is preferentially converted into axial expansion and bending deformation.

7. The hydraulically driven rigid-flexible coupling robotic arm according to claim 1, characterized in that: The rigid robotic arm structure (100) includes a base (101), a large arm (103), a small arm (104), a small arm hydraulic cylinder (121), a large arm hydraulic cylinder (122), and a shoulder hydraulic cylinder (123). The base (101) is installed in a fixed position. The base (101), the large arm (103), and the small arm (104) are connected in series and hinged. The base (101) and the large arm (103) are hinged together by a connecting bracket, and one end of the connecting bracket is hinged. At the end of the base (101), the cylinder body of the shoulder hydraulic cylinder (123) is located in the base (101) and its root end is synchronously connected to one end of the connecting bracket and the hinge position of the base (101), so that one end of the connecting bracket rotates about the vertical joint axis at its hinge position with the base (101); the other end of the connecting bracket is synchronously connected to the root end of the boom (103) through a hinged connecting rod, and the cylinder body of the boom hydraulic cylinder (122) is located in the boom (103). The base of the boom hydraulic cylinder (122) is hinged to the middle of the boom (103), and the end piston rod of the boom hydraulic cylinder (122) is synchronously connected to the hinge position of the connecting bracket and the connecting rod, so that the boom (103) rotates around the horizontal joint axis at the hinge position of the connecting bracket and the connecting rod; the cylinder body of the arm hydraulic cylinder (121) is located in the boom (103) and its base is hinged to the middle of the boom (103), and the end piston rod of the arm hydraulic cylinder (121) is synchronously connected to the boom (103) and the arm hydraulic cylinder (121). At the hinge position of the arm (104), the forearm (104) rotates about the horizontal joint axis at the hinge position with the upper arm (103); the end of the forearm (104) is equipped with a flexible joint unit (200) through a connector (300); the forearm hydraulic cylinder (121), the upper arm hydraulic cylinder (122) and the shoulder hydraulic cylinder (123) are connected; angle encoders are installed at the hinge positions of the base (101), the upper arm (103) and the forearm (104).

8. The hydraulically driven rigid-flexible coupled robotic arm according to claim 1, characterized in that: The hydraulic power unit is connected to the rigid robotic arm structure (100) and the flexible joint unit (200) through a valve-controlled drive branch and a volume control branch, respectively. The valve-controlled drive branch and the volume control branch share a hydraulic power source. The valve-controlled drive branch regulates the hydraulic flow into the rigid robotic arm structure (100), and the volume control branch regulates the fluid injection and recovery into the flexible joint unit (200). Pressure sensors are installed in both the valve-controlled drive branch and the volume control branch.

9. The collaborative control method for a hydraulically driven rigid-flexible coupled robotic arm according to any one of claims 1-8, characterized in that, include: The rigid-flexible coupling robotic arm is controlled by a distributed real-time control system, which includes a host computer and a lower-level real-time controller. The lower-level real-time controller collects pressure sensor signals transmitted by pressure sensors in real time to obtain pressure feedback from the forearm hydraulic cylinder (121), the upper arm hydraulic cylinder (122), the shoulder hydraulic cylinder (123), and each hydraulic drive cavity (206). It also collects angle encoder signals transmitted by angle encoders in real time to obtain the poses of each joint of the rigid robotic arm structure (100), and transmits them to the host computer as the system status. At the same time, it uses a motion capture system camera to obtain the position of each motion capture calibration ball (211) in the flexible joint unit (200) to determine the actual pose of the end of the flexible joint unit (200). The signal is transmitted to the host computer. The host computer sends a control signal to the lower real-time controller based on the target pose of the end of the flexible joint unit (200) of the rigid-flexible coupling manipulator. The lower real-time controller outputs valve control command and volume control command to the valve control drive branch and volume control branch of the hydraulic power unit, respectively. First, it controls the arm hydraulic cylinder (121), upper arm hydraulic cylinder (122) and shoulder hydraulic cylinder (123) of the rigid manipulator structure (100) in real time to move the flexible joint unit (200) to the vicinity of the target working area to complete the macro positioning. Then, it controls the pressure of each hydraulic drive cavity (206) of the flexible joint unit (200) in real time to make the attitude fine adjustment, so that the end of the flexible joint unit (200) moves to the target pose to perform the operation.

10. The collaborative control method for a hydraulically driven rigid-flexible coupled robotic arm according to claim 9, characterized in that: The flexible joint unit (200) adopts single-branch independent drive, multi-branch differential drive and multi-branch synchronous drive modes. In the single-branch independent drive mode, working medium is injected into a single hydraulic drive cavity (206), and the flexible joint unit (200) deflects in a single bending plane. In the multi-branch differential drive mode, working medium is injected differentially into multiple adjacent hydraulic drive cavities (206), and the flexible joint unit (200) forms a composite bending direction. In the multi-branch synchronous drive mode, equal amounts of working medium are injected into multiple hydraulic drive cavities (206) simultaneously, and the flexible joint unit (200) produces axial elongation or compliant adjustment while maintaining an approximately straight posture.

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