A method for controlling a single-leg hydraulically assisted exoskeleton, its control device, and the exoskeleton.

Abstract

This invention discloses a control method, control device, and exoskeleton for a single-leg hydraulically assisted exoskeleton. The control method involves parallel coordinated pump control and valve control components for each joint. The pump control component includes a variable pump control oil source and two two-way switching valves that determine the direction of the variable pump control oil source's outlet flow. The valve control component includes a hydraulic oil source and four two-way electro-hydraulic servo valves. Two electro-hydraulic servo valves control the flow of hydraulic oil from the hydraulic source to the two chambers of the corresponding hydraulic cylinder, while the other two electro-hydraulic servo valves control the flow from the two chambers of the corresponding hydraulic cylinder to the oil tank. The desired flow rates of the rod-side chamber and rodless chamber of each joint are calculated, thereby distributing the pump and valve flow rates to each joint. This invention effectively overcomes the effects of strong coupling between multiple joints, high-order nonlinearity of the hydraulic actuator, and model uncertainty in single-leg hydraulically assisted exoskeletons. It achieves good tracking and assistance of human movement, reduces system energy consumption, and achieves a longer operating time.

Description

Technical Field

[0001] This invention relates to an exoskeleton control method and control device in the field of exoskeletons, and more particularly to a single-leg hydraulically assisted exoskeleton control method, a single-leg hydraulically assisted exoskeleton control device for implementing the single-leg hydraulically assisted exoskeleton control method, and an exoskeleton employing the single-leg hydraulically assisted exoskeleton control method. Background Technology

[0002] Wearable lower limb assistive exoskeletons are human-machine integrated devices that enhance the wearer's load-bearing capacity and can be used in emergency rescue, national defense, and other fields. Hydraulic actuators, due to their advantages of high output force and torque, and high power-to-weight ratio, are well-suited for compact, heavy-duty systems like lower limb assistive exoskeletons. In assistive exoskeleton systems, reducing human-machine interaction forces allows the exoskeleton to accurately track the wearer's movements, enabling the wearer to easily bear weight. Therefore, high-precision human-machine interaction force control algorithm design is crucial for realizing the exoskeleton's assistive function. On the other hand, the energy supply system of lower limb assistive exoskeletons must be carried by the wearer, and the energy source is very limited. To ensure a long working time, system energy efficiency cannot be ignored. Achieving both high-precision and high-efficiency control of lower limb hydraulic assistive exoskeletons is a key technology for improving exoskeleton performance.

[0003] Achieving high-precision, high-efficiency control of hydraulic exoskeletons requires addressing two key issues. First, it necessitates the design of a high-precision, high-efficiency electro-hydraulic system for the exoskeleton. Second, it requires designing a corresponding high-precision, high-efficiency control algorithm based on the selected electro-hydraulic system. However, traditional lower limb hydraulic-assisted exoskeleton electro-hydraulic systems often employ valve-controlled systems. Due to throttling and overflow losses, traditional hydraulic exoskeletons suffer from low energy efficiency. Furthermore, existing hydraulic-assisted exoskeleton control methods primarily address the inherent strong coupling and high-order nonlinearity of hydraulic exoskeleton systems, as well as the impact of modeling uncertainties. These methods only achieve high-precision force control without considering energy consumption, resulting in significant system energy consumption. Summary of the Invention

[0004] To address the technical problems of high-order nonlinearity, model uncertainty, and high energy consumption in existing single-leg hydraulically assisted exoskeletons, this invention provides a control method for a single-leg hydraulically assisted exoskeleton, a control device for implementing the control method, and an exoskeleton employing the control method.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a control method for a single-leg hydraulically assisted exoskeleton, used to control the movement of a single-leg hydraulically assisted exoskeleton; the control method includes the following steps:

[0006] The three hydraulic systems applied to the ankle, knee, and hip joints of the exoskeleton respectively all adopt parallel pump-valve coordinated electro-hydraulic systems. Each parallel pump-valve coordinated electro-hydraulic system includes a parallel coordinated pump control part and a valve control part. The pump control part includes a variable pump control oil source PS1 and two two-way switching valves SV1 and SV2 that determine the direction of the outlet flow of the variable pump control oil source PS1. The valve control part includes four two-way electro-hydraulic servo valves PV1, PV2, PV3, and PV4 and a hydraulic oil source PS2. The electro-hydraulic servo valves PV1 and PV2 control the flow of hydraulic oil source PS2 to the two chambers of the corresponding hydraulic cylinders, and the electro-hydraulic servo valves PV3 and PV4 control the flow of hydraulic oil from the two chambers of the corresponding hydraulic cylinders to the oil tank.

[0007] For the parallel pump-valve coordinated electro-hydraulic system of each joint in a single-leg hydraulically assisted exoskeleton, based on the reference rotation angle of each joint... Reference rotational angular velocity Reference angular acceleration The actual driving force F of the hydraulic cylinder L Actual rotation angle q, actual rotation angular velocity The desired flow rate α of the rod cavity of each joint is obtained. 2p =[α 2p1 α 2p2 α 2p3 ] T And the expected flow rate Q of the rodless cavity 1m =[Q 1m1 Q 1m2 Q 1m3 ] T Where i represents the sequence number of the three joints, the expected flow rate of the rod cavity of the i-th joint is α. 2pi The expected flow rate of the rodless cavity of the i-th joint is Q. 1mi ;

[0008] According to α 2p Q 1m Calculate the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint to distribute the pump and valve flow to each joint.

[0009] The single-leg hydraulic assistive exoskeleton control method of this invention employs a hydraulic system characterized by its small size, light weight, flexible layout, compact structure, ability to output significant force or torque, sensitive action response, and ease of control. The hydraulic system utilizes a parallel pump-valve coordinated electro-hydraulic system scheme, allowing the pump control section to provide the main flow and the valve control section to provide a minor flow, thus improving the energy efficiency of the lower limb assistive exoskeleton electro-hydraulic system. The single-leg hydraulic assistive exoskeleton control method of this invention employs a force control approach, utilizing an adaptive robust control algorithm (ARC) to design the upper and lower level controllers, effectively overcoming the influence of high-order nonlinearity and model uncertainty inherent in single-leg hydraulic assistive exoskeletons. In the lower level controller, the rodless chamber of the hydraulic cylinder employs position tracking control, while the rod chamber employs pressure tracking control, solving the technical problem of high energy consumption in existing exoskeleton control methods. This not only achieves excellent tracking and assistance of human movement with the hydraulic assistive exoskeleton but also reduces system energy consumption, achieving a longer operating time and demonstrating strong application value. This invention effectively overcomes the effects of strong multi-joint coupling, high-order nonlinearity of hydraulic actuators, and model uncertainty in single-leg hydraulically assisted exoskeletons. It not only achieves good tracking and assistance of human movement by hydraulically assisted exoskeletons, but also reduces system energy consumption and achieves a longer battery life.

[0010] The present invention also provides a single-leg hydraulically assisted exoskeleton, which adopts the above-mentioned control method for any single-leg hydraulically assisted exoskeleton.

[0011] The present invention also provides a single-leg hydraulically assisted exoskeleton control device, which employs any of the above-mentioned single-leg hydraulically assisted exoskeleton control methods, the control device comprising:

[0012] Three parallel pump-valve coordinated electro-hydraulic systems are respectively applied to the ankle, knee, and hip joints of the exoskeleton. Each parallel pump-valve coordinated electro-hydraulic system includes a parallel coordinated pump control part and a valve control part. The pump control part includes a variable pump control oil source PS1 and two two-way switching valves SV1 and SV2 that determine the direction of the outlet flow of the variable pump control oil source PS1. The valve control part includes four two-way electro-hydraulic servo valves PV1, PV2, PV3, and PV4 and a hydraulic oil source PS2. The electro-hydraulic servo valves PV1 and PV2 control the flow of hydraulic oil source PS2 to the two chambers of the corresponding hydraulic cylinders, and the electro-hydraulic servo valves PV3 and PV4 control the flow of hydraulic oil from the two chambers of the corresponding hydraulic cylinders to the oil tank.

[0013] The flow acquisition module is used to coordinate the electro-hydraulic system with parallel pumps and valves for each joint of the single-leg hydraulically assisted exoskeleton, based on the reference rotation angle of each joint. Reference rotational angular velocity Reference angular acceleration The actual driving force F of the hydraulic cylinder L Actual rotation angle q, actual rotation angular velocity The desired flow rate α of the rod cavity of each joint is obtained. 2p =[α 2p1 α 2p2 α 2p3 ] T And the expected flow rate Q of the rodless cavity 1m =[Q 1m1 Q 1m2 Q 1m3 ] T Where i represents the sequence number of the three joints, the expected flow rate of the rod cavity of the i-th joint is α. 2pi The expected flow rate of the rodless cavity of the i-th joint is Q. 1mi ;

[0014] The control voltage acquisition module is used to determine the voltage based on α. 2p Q 1m Calculate the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint to distribute the pump and valve flow to each joint.

[0015] Compared to existing exoskeleton control methods, the single-leg hydraulically assisted exoskeleton control method and control device of the present invention have the following beneficial effects:

[0016] 1. The single-leg hydraulically assisted exoskeleton control method uses a hydraulic drive system for its exoskeleton drive system, which has the characteristics of being able to output large force or torque, having sensitive action response, being easy to control, having small size, and having a compact structure.

[0017] 2. The control method for this single-leg hydraulic assistive exoskeleton adopts a parallel pump-valve coordinated electro-hydraulic system scheme, constructing an independently operating pump control part and valve control part, allowing the pump control part to provide the main flow and the valve control part to provide the minor flow, thereby improving the energy efficiency of the lower limb assistive exoskeleton electro-hydraulic system without sacrificing accuracy.

[0018] 3. The single-leg hydraulically assisted exoskeleton control method uses a sensor system consisting mainly of a back force sensor and a joint encoder to achieve reliable human-machine interaction.

[0019] 4. This single-leg hydraulically assisted exoskeleton control method employs a force control approach. An Adaptive Robust Control (ARC) algorithm is used to design the upper and lower level controllers, effectively overcoming the influence of high-order nonlinearity and model uncertainty inherent in single-leg hydraulically assisted exoskeletons. In the lower level controller, the rodless chamber of the hydraulic cylinder uses position tracking control, while the rod chamber uses pressure tracking control, ensuring that the pressure in one chamber of the hydraulic cylinder is always at its minimum. This solves the technical problem of high energy consumption in existing exoskeleton control methods. It not only achieves excellent tracking and assistance of human movement with the hydraulically assisted exoskeleton but also reduces system energy consumption and achieves a longer operating time, demonstrating strong application value.

[0020] 5. This single-leg hydraulically assisted exoskeleton control method uses human movement as the external input for the entire exoskeleton system, ensuring balance during walking. Furthermore, it employs a cascaded force control algorithm to enable the exoskeleton to follow the human's trajectory. The control method is simple to implement, easy to engineer, and offers flexible control.

[0021] 6. The beneficial effects of this single-leg hydraulic assist exoskeleton control device are the same as those of the single-leg hydraulic assist exoskeleton control method described above. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall shape and structure of a single-leg hydraulically assisted exoskeleton provided in a preferred embodiment of the present invention.

[0023] Figure 2 for Figure 1 The schematic diagram of the single-joint parallel pump-valve coordinated electro-hydraulic system used in the single-leg hydraulic power exoskeleton.

[0024] Figure 3 for Figure 1 A schematic diagram illustrating the design concept of the single-leg hydraulic power-assisted exoskeleton control method.

[0025] Figure 4 for Figure 1 The control flowchart of the single-leg hydraulic power-assisted exoskeleton control method used in the single-leg hydraulic power-assisted exoskeleton. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Please see Figure 1 This is a schematic diagram of the overall shape and structure of a single-leg hydraulically assisted exoskeleton provided in a preferred embodiment of the present invention. Figure 1As can be seen from the diagram, this single-leg hydraulically assisted exoskeleton includes: 1. Foot component; 2. Ankle joint encoder; 3. Ankle joint hydraulic cylinder with rod chamber pressure sensor; 4. Ankle joint hydraulic cylinder with rodless chamber pressure sensor; 5. Lower leg component; 6. Knee joint encoder; 7. Knee joint hydraulic cylinder with rod chamber pressure sensor; 8. Thigh component; 9. Knee joint hydraulic cylinder; 10. Knee joint hydraulic cylinder with rodless chamber pressure sensor; 11. Hip joint encoder; 12. Hip joint hydraulic cylinder with rod chamber pressure sensor; 13. Hip joint hydraulic cylinder with rodless chamber pressure sensor. 4. Base plate 15. Hip joint hydraulic cylinder 16. Ankle joint pump control unit switch valve 17. Ankle joint valve control unit servo valve 18. Knee joint pump control unit switch valve 19. Knee joint valve control unit servo valve 20. Hip joint pump control unit switch valve 21. Hip joint valve control unit servo valve 22. Back plate 23. Back force sensor 24. Back strap 25. Waist strap 26. Servo amplifier board (not shown in the figure), variable speed pumps corresponding to each joint (not shown in the figure), real-time controller (not shown in the figure).

[0028] The foot 1 of the exoskeleton serves as the contact part with the ground, supporting the entire exoskeleton and functioning similarly to a human foot. The bottom end of the lower leg member 6 is rotatably connected to the foot 1, which can be a hinge connection. The bottom end of the thigh member 9 is rotatably connected to the top end of the lower leg member 6, which can also be a hinge connection. The ankle joint hydraulic cylinder 4 drives relative rotation between the foot 1 and the lower leg member 6. The ankle joint encoder 2 is mounted at the ankle joint (it can be mounted at the hinge connection). The knee joint hydraulic cylinder 10 drives relative rotation between the lower leg member 6 and the thigh member 9. The knee joint encoder 7 is mounted at the knee joint (it can be mounted at the hinge connection). The top end of the thigh member 9 is rotatably connected to the base plate 9, and the hip joint hydraulic cylinder 16 drives relative rotation between the thigh member 9 and the base plate 15. The hip joint encoder 12 is mounted at the hip joint (it can be mounted at the hinge connection). The base plate 15 and the back plate 23 are connected by bolts. The back force sensor 24 is installed between the back plate 23 and the back strap 25. The waist strap 26 is connected to the lower end of the back plate 23.

[0029] Ankle joint hydraulic cylinder rod chamber pressure sensor 3 is used to detect the rod chamber pressure of ankle joint hydraulic cylinder 4, and rodless chamber pressure sensor 5 is used to detect the rodless chamber pressure of ankle joint hydraulic cylinder 4. Ankle joint encoder is used to detect the rotation angle at the ankle joint. Knee joint hydraulic cylinder rod chamber pressure sensor 8 is used to detect the rod chamber pressure of knee joint hydraulic cylinder 10, and rodless chamber pressure sensor 11 is used to detect the rodless chamber pressure of knee joint hydraulic cylinder 10. Knee joint encoder is used to detect the rotation angle at the knee joint. Hip joint hydraulic cylinder rod chamber pressure sensor 13 is used to detect the rod chamber pressure of hip joint hydraulic cylinder 16, and rodless chamber pressure sensor 14 is used to detect the rodless chamber pressure of hip joint hydraulic cylinder 16. Hip joint encoder is used to detect the rotation angle at the hip joint.

[0030] The switching valve 17 of the ankle joint pump control section and the servo valve 18 of the ankle joint valve control section are used to control the ankle joint hydraulic cylinder 4. The switching valve 19 of the knee joint pump control section and the servo valve 20 of the knee joint valve control section are used to control the knee joint hydraulic cylinder 10. The switching valve 21 of the hip joint pump control section and the servo valve 22 of the hip joint valve control section are used to control the hip joint hydraulic cylinder 16. The real-time controller is electrically connected to the following components: ankle encoder 2, ankle hydraulic cylinder rod chamber pressure sensor 3, ankle hydraulic cylinder rodless chamber pressure sensor 5, knee encoder 7, knee hydraulic cylinder rod chamber pressure sensor 8, knee hydraulic cylinder rodless chamber pressure sensor 11, hip encoder 12, hip hydraulic cylinder rod chamber pressure sensor 13, hip hydraulic cylinder rodless chamber pressure sensor 14, ankle pump control unit switching valve 17, ankle valve control unit servo valve 18, knee pump control unit switching valve 19, knee valve control unit servo valve 20, hip pump control unit switching valve 21, hip valve control unit servo valve 22, and back force sensor 24. The real-time controller model can be an NI cRIO-9031 product, but is not limited to this. The servo valve amplifier board can be a Star WO36829 / 1 product, but is not limited to this.

[0031] To overcome the high energy consumption of the electro-hydraulic system in a single-leg hydraulically assisted exoskeleton, a parallel pump-valve coordinated electro-hydraulic system scheme is adopted. This involves constructing independently operating pump-control and valve-control sections, with the pump-control section providing the main flow and the valve-control section providing a minor flow. To overcome the influence of high-order nonlinearity and model uncertainty in the single-leg hydraulically assisted exoskeleton, and to achieve good tracking and assistance of human movement, the design is optimized.

[0032] In this embodiment, the present invention modifies the original power systems of the ankle, knee, and hip joints, improving the original power system of each joint into a parallel pump-valve coordinated electro-hydraulic system. Please refer to the following: Figure 2Each parallel pump-valve coordinated electro-hydraulic system includes a parallel coordinated pump control section and a valve control section; the pump control section includes a variable pump control oil source PS1 and two two-way switching valves SV1 and SV2 that determine the direction of the outlet flow of the variable pump control oil source PS1; the valve control section includes four two-way electro-hydraulic servo valves PV1, PV2, PV3 and PV4 and a hydraulic oil source PS2. The electro-hydraulic servo valves PV1 and PV2 control the flow of hydraulic oil source PS2 to the two chambers of the corresponding hydraulic cylinder, and the electro-hydraulic servo valves PV3 and PV4 control the flow of hydraulic oil from the two chambers of the corresponding hydraulic cylinder to the oil tank.

[0033] This invention not only improves the power systems of the ankle, knee, and hip joints, but also requires a corresponding single-leg hydraulically assisted exoskeleton control method to complete the coordinated movements between these three joints. The single-leg hydraulically assisted exoskeleton control method in this invention employs an adaptive robust control algorithm (ARC) that effectively overcomes the influence of model uncertainties. Its principle is to continuously adjust the system model parameters by designing an adaptive rate, perform feedforward compensation on the control model to ensure zero tracking error under static conditions, and design robust feedback to ensure the dynamic characteristics and stability of the single-leg hydraulically assisted exoskeleton system. Simultaneously, using a cascaded force control method, an upper-level controller obtains the reference trajectory of the single-leg exoskeleton, while a lower-level rodless cavity position tracking controller, a lower-level rod-cavity pressure planner, and a lower-level rod-cavity pressure tracking controller track the reference trajectory and reduce system energy consumption. The control algorithm is simple to implement, easy to engineering, and offers flexible control.

[0034] In practical applications, the single-leg hydraulic-assisted exoskeleton control method can be implemented in software form, such as as a standalone program installed on a computer terminal (e.g., computer, smartphone, control system, or other IoT device); or as an embedded program installed on a computer terminal, such as a microcontroller. A computer terminal typically includes memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the program to implement the steps of the single-leg hydraulic-assisted exoskeleton control method. Alternatively, the single-leg hydraulic-assisted exoskeleton control method can be applied in software form, such as as a standalone program that runs on a computer-readable storage medium (e.g., a USB flash drive, or a USB security token), with the program triggered externally. A USB flash drive is a type of computer-readable storage medium that stores a computer program. When the program is executed by the processor, it implements the steps of the single-leg hydraulic-assisted exoskeleton control method.

[0035] Regardless of the specific application of the single-leg hydraulic power-assisted exoskeleton control method, functionally, it can be categorized as a single-leg hydraulic power-assisted exoskeleton control device. This device primarily includes a flow rate acquisition module, a control voltage acquisition module, a hydraulic cylinder actual driving force acquisition module, a joint actual driving torque acquisition module, and a rotational angular velocity acquisition module.

[0036] Next, combined Figure 3 and Figure 4 The single-leg hydraulically assisted exoskeleton control method of the present invention will be described in detail below. When applying the single-leg hydraulically assisted exoskeleton control method, the exoskeleton needs to be prepared in advance as follows:

[0037] (1) The exoskeleton is fixed to the human body by the back strap 25 and the waist strap 26. The sampling period T of the real-time controller is initialized according to the actual situation. The range of the sampling period T is between 10 and 20 milliseconds.

[0038] (2) Rotate foot 1 to a horizontal position, rotate calf rod 6, thigh rod 9 and back plate 23 to a vertical position. At this time, initialize ankle encoder 2, knee encoder 7 and hip encoder 12, and zero the value of the joint encoder.

[0039] (3) Initialize the back force sensor 24 and zero the value of the back force sensor 24;

[0040] (4) Design the principle scheme of the pump valve coordinated electro-hydraulic system for a single-leg hydraulically assisted exoskeleton.

[0041] The principle and solution of the pump-valve coordinated electro-hydraulic system for a single-leg hydraulically assisted exoskeleton are as follows: Figure 2 As shown, Figure 2 The schematic diagram shows a single-joint parallel pump-valve coordinated electro-hydraulic system. The principle of the single-leg hydraulically assisted exoskeleton is to apply the single-joint parallel pump-valve coordinated electro-hydraulic system to the ankle, knee and hip joints of the exoskeleton.

[0042] The parallel pump-valve coordinated electro-hydraulic system is mainly divided into a pump control section and a valve control section. The pump control section consists of one variable pump control oil source PS1 and two two-way switching valves SV1 and SV2. The direction of the oil source's outlet flow is determined by the switching valves. The valve control section consists of four two-way electro-hydraulic servo valves PV1, PV2, PV3, and PV4 and the hydraulic oil source PS2. Electro-hydraulic servo valves PV1 and PV2 control the flow of oil from the oil source to the two chambers of the hydraulic cylinder, while electro-hydraulic servo valves PV3 and PV4 control the flow of oil from the two chambers of the hydraulic cylinder to the oil tank. The oil source for the pump control section is not limited to variable speed pumps; similar variable pumps, as well as combinations of variable speed and variable pumps, can also be used. These require real-time adjustment of the output flow based on a given input signal. PV1, PV2, PV3, and PV4 are not limited to electro-hydraulic servo valves; similar proportional servo valves and proportional cartridge valves can also be used in the valve control section. Their basic function is to continuously regulate the flow through the valve orifice, with a bandwidth higher than that of the pump control section. The flow rate of the pump control section and the flow rate of the valve control section are superimposed in parallel at N1 and N2, and together they control the flow rate to the two chambers of the hydraulic cylinder.

[0043] (5) Establish a physical model of a single-leg hydraulically assisted exoskeleton and convert it into a state equation; wherein, the physical model includes a human-machine interface model, a motion model of the exoskeleton mechanical body, and a dynamic model of the hydraulic actuator.

[0044] The expression for the upper-level human-computer interface model is:

[0045]

[0046] Among them, F hm =]F hmx F hmy τ hmz ] T The human-machine interaction force at the point of contact between the human and the exoskeleton robot, where x, y, and z represent the symbols of the three coordinate axes of the world coordinate system; K = diag{K x ,K y ,K z} represents the stiffness of the human-machine interface, x h =[x hx x hy x hz ] T It is the Cartesian coordinate position of the contact point of the strap on the back of the person, x e =[x ex x ey x ez ] T It is the Cartesian position of the contact point 23 on the exoskeleton backplate; It concerns the concentrated interference and modeling uncertainty of human-machine interfaces.

[0047] When transforming the physical model, the integral of the human-machine interaction force is used. Replace F hm The state equation is obtained as follows:

[0048]

[0049] The motion model of the exoskeleton mechanical body is as follows:

[0050]

[0051] In the formula, τ act =[τ1 τ2 τ3] T Let be the joint driving torque at the ankle, knee, and hip joints, J be the Jacobian matrix of the system at the force sensor, and q = [q1 q2 q3]. T These represent the rotation angles of the ankle, knee, and hip joints, respectively. sp3 (q) is the system's inertia matrix. It is the system's centrifugal force and Coriolis force matrix, G sp3 (q) is the gravity matrix of the system, and B = diag{B1,B2,B3} is the damping matrix of the system. It is a concentrated interference in the system;

[0052] The dynamic model of the hydraulic actuator is as follows:

[0053]

[0054]

[0055]

[0056] Q 1i =Q 1vi +Q 1pi Q 2i =Q 2vi -Q 2pi

[0057] Q 1vi =Q pv1i -Q pv3i Q 2vi =-Q pv2i +Q pv4i

[0058]

[0059]

[0060] x pvji =u pvji i = 1, 2, 3

[0061] Q 1pi =sw 1i Q pi Q 2pi =sw 2i Q pi

[0062]

[0063] Q pi =k pi u pi i = 1, 2, 3

[0064] In the formula x Li It is the displacement of hydraulic cylinder i. It is x Li Regarding q i First-order partial derivative, P 1i and P 2i A represents the actual pressure in the rodless chamber and the rod chamber of hydraulic cylinder i. 1i and A 2i V represents the effective area of ​​the rodless chamber and the rod chamber in hydraulic cylinder i. 1i =V h1i +A 1i x Li and V 2i =V h2i -A 2i x Li These are the total volumes of the two chambers within hydraulic cylinder i, V h1i V h2i It is q i When β = 0, the volume of the two chambers of hydraulic cylinder i, β e Q represents the bulk modulus of elasticity. 1i Q 2i These are the oil inlet flow rate of the rodless chamber and the oil outlet flow rate of the rod chamber in hydraulic cylinder i, respectively. and Q represents the lumped modeling error and uncertain disturbances in the dynamic model of the hydraulic actuator. 1vi and Q 2vi Q represents the inlet flow rate of the rodless chamber and the outlet flow rate of the rod chamber in hydraulic cylinder i, respectively, from the valve-controlled section. 1pi and Q 2pi Q represents the oil inlet flow rate from the rodless chamber and the rod chamber of the pump control unit in hydraulic cylinder i, respectively. pvji k represents the flow rate of the j-th servo valve corresponding to hydraulic cylinder i. qpvji Let x be the flow gain coefficient of the j-th servo valve corresponding to hydraulic cylinder i. pvji P represents the valve core displacement of the j-th servo valve corresponding to hydraulic cylinder i. s With P rThese are the oil supply pressure of the valve control section and the oil tank pressure, u pvji Q is the control voltage of the j-th servo valve corresponding to hydraulic cylinder i. pi k represents the output flow rate of the variable speed pump corresponding to hydraulic cylinder i. pi and u pi These represent the flow gain coefficient and control voltage of the variable speed pump corresponding to hydraulic cylinder i, respectively.

[0065] The method of converting a physical model into state equations includes the following steps:

[0066] (5.1) Define state variables:

[0067]

[0068] x2 = q

[0069]

[0070] x4=P1=[P 11 P 12 P 13 ] T

[0071] x5=P2=[P 21 P 22 P 23 ] T

[0072] x=[x1 T x2 T x3 T x4 T x5 T ] T

[0073] Define the uncertainty of a lumped model as:

[0074]

[0075]

[0076]

[0077]

[0078] (5.2) The uncertainty of the lumped model is divided into two parts: a constant and a time-varying function, resulting in: and Δ i Represent The constant part and the time-varying part;

[0079] (5.3) Let in, Δ 1n =[Δ 1nx Δ 1ny Δ 1nz ] T ,β=[Y2 Y3 Y4 X4 J2 J3 J4] T For the system parameters of a single leg of the exoskeleton, B θ =[B1 B2 B3] T For system damping, Δ 2n =[Δ 2n1 Δ 2n2 Δ 2n3 ] T Δ 3n =[Δ 3n1 Δ 3n2 Δ 3n3 ] T θ β =β e θ Q2i =-β e D 32ni .

[0080] The state equation of the physical model of the single-leg hydraulically assisted exoskeleton is:

[0081]

[0082]

[0083]

[0084]

[0085] Q v =N1Q1+N2Q2

[0086] in, A1=diag{A 11 A 12 A 13}, A2=diag{A 21 A 22 A 23}, F L =A1P1-A2P2, Q v =[Q 11 A 11 / V 11 +Q 21 A 21 / V 21 Q 12 A 12 / V 12 +Q22 A 22 / V 22 Q 13 A 13 / V 13 +Q 23 A 23 / V 23 ] T Q1 = [Q 11 Q 12 Q 13 ] T Q2=[Q 21 Q 22 Q 23 ] T N1 = diag{A 11 / V 11 A 12 / V 12 A 13 / V 13}, N2=diag{A 21 / V 21 A 22 / V 22 A 23 / V 23},

[0087] (6) The wearer is connected to the back force sensor 24 via the back strap 25, and the human-machine interaction force of the back force sensor 24 is measured. The reference rotation angle of each joint of the single-leg hydraulic assist exoskeleton is obtained through the upper controller.

[0088] Based on the state equation of the physical model in step (5), let the first tracking error be z1 = x1 - x 1d , where x 1d It is the integral of the expected human-machine interaction force in the x, y, z directions, and takes a value of zero; let x e Treat it as a virtual control input, denoted as x. e Design control law x m This causes the first tracking error z1 of the human-machine interaction force to rapidly approach zero;

[0089] Let x m =x ma +x ms +x msn ,in x ms =K1z1, and It is made by x ma After parameter linearization, the following was obtained: It is the expected human-machine interaction force in the x, y, z directions, K1=diag{K 1x ,K 1y ,K 1z} is the linear feedback gain, and in this example, K1 = diag{8,8,8}; It is θ F The estimated value, and the range of the estimated value is: In this embodiment, the initial value is taken as in For parameter θ F The estimated value The minimum value, For parameter θ F The estimated value The maximum value; in this embodiment, take the maximum value. estimated value The upper-level controller is composed of adaptive rate We obtain Γ1, which is a positive definite gain matrix. In this embodiment, we take Γ1 = diag{0,0,0,2,15,2}. The mapping function is:

[0090]

[0091] In the formula, · i The independent variable is the nonlinear robust feedback term x. msn satisfy:

[0092]

[0093]

[0094] in, It is an estimated value. Subtract the actual value θ F , ε1 is the threshold and is any non-negative number. In this example, we take ε1 = [1 1 1]. T x msn =[0 0 0] T .

[0095] According to the design x m And the inverse kinematics model of a single-leg hydraulically assisted exoskeleton, to obtain the desired rotation angle q of each joint of the exoskeleton. m =[q m1 q m2 q m3 ] T :

[0096] q m =invkine(x m )

[0097] Here, invkine represents inverse kinematics. This is based on the desired rotation angle q of each joint of the exoskeleton. mi Let i = 1, 2, 3, and then smooth the data using a fourth-order filter to obtain the reference rotation angle, reference rotation angular velocity, reference rotation angular acceleration, and reference rotation angular jerk for each joint of the exoskeleton. The state equation of the fourth-order filter is as follows:

[0098]

[0099]

[0100]

[0101]

[0102] i = 1, 2, 3

[0103] In the formula, These represent the filtered reference rotation angle, reference rotation angular velocity, reference rotation angular acceleration, and reference rotation angular jerk, respectively, from q mi To η 1i The transfer function is

[0104]

[0105] Using the transfer function described above, we obtain q. mi Transformed into the required smooth exoskeleton, each joint reference rotation angle η 1i The values ​​of a1, a2, a3, and a4 in the transfer function are obtained through pole placement. In this embodiment, the closed-loop poles are set to 20 radians per second, resulting in the values ​​of a1, a2, a3, and a4 as a1 = 80, a2 = 2400, a3 = 32000, and a4 = 160000, respectively. However, these values ​​are not necessarily limited to these values ​​in practice.

[0106] (7) Obtain the actual rotation angle values ​​of each joint of the single-leg hydraulically assisted exoskeleton through the ankle joint encoder 2, knee joint encoder 7 and hip joint encoder 12; obtain the reference rotation angle of each joint according to step (6), and use the actual rotation angle and the reference rotation angle as the input of the lower rodless cavity position tracking controller. The output of the lower rodless cavity position tracking controller is the desired driving force and the desired flow rate of the rodless cavity at the ankle joint hydraulic cylinder 4, knee joint hydraulic cylinder 9 and hip joint hydraulic cylinder 16 in the single-leg hydraulically assisted exoskeleton; the design method of the lower rodless cavity position tracking controller includes the following steps:

[0107] Let the second tracking error be... in Define a transformation equation:

[0108]

[0109]

[0110] Where K2 is the positive definite feedback gain matrix, and in this example, K2 is taken as diag{85,85,85}. z3 is the third tracking error, and the transfer functions of z2 and z3 are G. p (s)=z2(s) / z3(s)=diag{1 / (s+K 2i ),i=1,2,3},

[0111] Let Bx3 = Y B B θ , Where β = [Y2 Y3 Y4 X4 J2 J3 J4] T Y2, Y3, Y4, X4, J2, J3, J4 are all model parameters of the mechanical structure. B θ =[B1 B2 B3] T For the system's damping;

[0112] (7.1) F L Treat it as a virtual control input, which is F L Design control law F Ld This causes the second tracking error z2 to rapidly approach zero;

[0113] Let F Ld =F Lda +F Lds +F Ldsn ,in, F Lds =-h -1 K3z3, where K3 is the linear feedback gain. In this example, K3 is set to diag{85,85,85}. It is about the parameters β, B θ ,Δ 2n The estimated value of θ. q =[β T B θ T Δ 2n T β e Δ 3n T ] T In this example, we take the initial value. It is θ q The estimated value, and the range of the estimated value is: in For parameter θ q The estimated value The minimum value, For parameter θ q The estimated value The maximum value; in this example, take estimated value The lower-level rodless cavity position tracking controller is equipped with an adaptive rate. We obtain τ4 from step (7.3), and Γ2 is the positive definite gain matrix. In this example, we take...

[0114] Γ2=diag{10,0,0,0,10,0,0,0,0,0,0,0,0,0,0,0}, The mapping function is:

[0115]

[0116] In the formula, · i Let φ3 be the independent variable, and let φ3 = [-Y -Y B I 3×3 0 3×1 0 3×3 ] T , among which, I 3×3 =diag{1,1,1},0 3×1 =[0 0 0] T 0 3×3 =diag{0,0,0}, F Ldsn satisfy:

[0117]

[0118]

[0119] In the formula, It is an estimated value. Subtract the actual value θ q , ε2 is the threshold value and can be any non-negative number; in this example, ε2 is taken as [1 1 1]. T F Ldsn =[0 0 0] T .

[0120] (7.2) Design an adaptive robust observer to estimate the joint rotational angular velocity and angular acceleration.

[0121] Let the observation error be e. o1 = x² - y, where y is an estimated value of the joint angle. A transformation equation is defined as follows:

[0122]

[0123]

[0124] Among them, K o1 It is a positive definite feedback gain matrix. In this example, we take K. o1 =[60 60 60] T ; These are estimates of the joint's angular velocity and angular acceleration. Designed as follows:

[0125]

[0126] in, It uses θ q Another set of parameter estimates The obtained M sp3 C sp3 G sp3 The estimated value, K o2 It is a linear positive definite feedback gain matrix. In this example, we take K. o2 =[400 200 200] T ;K o2s It is a nonlinear positive definite feedback gain matrix. In this example, we take K. o2s =[0 0 0] T ;T os It is the robust feedback term for the observer error; let In this example, we take the initial value. The range of estimated values ​​can be obtained as follows: make estimated value In the adaptive robust observer, there is an adaptive rate We obtain, where Γ o It is a positive definite gain matrix. In this example, we take Γ. o =diag{10,0,0,0,2,0,0,0,0,0,0,0,0,0,0,0}, The mapping function is:

[0127]

[0128] In the formula, · i As the independent variable, The following two conditions must be met:

[0129]

[0130]

[0131] In the formula, It is an estimated value. Subtract the actual value θ q , ε o It is a threshold and can be any non-negative number. In this embodiment, ε is selected. o =[1 1 1] T Select T os =[0 0 0] T .

[0132] Define the fourth tracking error in, That is, in the control law F Ld Chinese replace To calculate

[0133] (7.3) Treat Q1 as a virtual control input and design a control law Q for Q1. 1m This results in the fourth tracking error It rapidly approaches zero;

[0134] Let Q 1m =Q 1ma +Q 1ms +Q 1msn ,in,

[0135]

[0136] φ 4c =[0 3×7 0 3×3 0 3×3 N2α 2p -q v I 3×3 ] T , α 2p From step (9)

[0137] get, K4 > 0 represents the linear feedback gain. In this example, we take K4 = [85 85 85]. T .

[0138] Let φ4 = [0 3×7 0 3×3 0 3×3 N1Q 1ma +N2α 2p -q v I 3×3 ] T , Q 1msnThe following two conditions must be met:

[0139]

[0140]

[0141] In the formula, It is an estimated value. Subtract the actual value θ q , ε3 is a threshold value and can be any non-negative number; in this embodiment, ε3 is chosen to be [1 1 1]. T Select Q 1msn =[0 0 0] T .

[0142] (8) The desired driving force of the ankle joint hydraulic cylinder 4, knee joint hydraulic cylinder 10 and hip joint hydraulic cylinder 16 in the single-leg hydraulically assisted exoskeleton obtained in step (7) is used as the input of the lower rod-cavity pressure planner. The output of the lower rod-cavity pressure planner is the desired rod-cavity pressure of the ankle joint hydraulic cylinder 4, knee joint hydraulic cylinder 10 and hip joint hydraulic cylinder 16 in the single-leg hydraulically assisted exoskeleton. The design of the lower rod-cavity pressure planner includes the following steps:

[0143] Considering that a good control design can ensure that the system error is within a small range, the model compensation term F in step (7.1) is... Lda It can basically characterize the desired driving force F Ld In addition, to obtain a more continuous and smooth desired pressure in the rod cavity and to avoid the negative impact of noise, a reference trajectory is used instead of the measurement signal of the state quantity.

[0144] set up

[0145] Among them, F Ldad =[F Ldad1 F Ldad2 F Ldad3 ] T .

[0146] The desired pressure p in the rod chamber of the i-th hydraulic cylinder 2di Designed as follows:

[0147]

[0148] In the formula, p c This is the set minimum working pressure; in this example, we take p. c =0.1×10 6 Pa. The derivative of the desired pressure in the rod chamber of the i-th hydraulic cylinder. Designed as follows:

[0149]

[0150] (9) Obtain the actual pressure values ​​of the rod chambers of the ankle joint hydraulic cylinder 4, knee joint hydraulic cylinder 10, and hip joint hydraulic cylinder 16 through the rod chamber pressure sensor 3 of the ankle joint hydraulic cylinder, the rod chamber pressure sensor 8 of the knee joint hydraulic cylinder, and the rod chamber pressure sensor 13 of the hip joint hydraulic cylinder; based on the expected pressure of the rod chambers of the ankle joint hydraulic cylinder 4, knee joint hydraulic cylinder 10, and hip joint hydraulic cylinder 16 in the single-leg hydraulic assist exoskeleton obtained in step (8), use the expected pressure of the rod chambers and the actual pressure of the rod chambers as the input quantities of the lower rod chamber pressure tracking controller, and the output of the lower rod chamber pressure tracking controller is the expected flow rate of the rod chambers of the ankle joint hydraulic cylinder 4, knee joint hydraulic cylinder 10, and hip joint hydraulic cylinder 16. In this example, the lower rod chamber pressure tracking controller method includes the following steps:

[0151] Define the fifth tracking error z 5i =p 2i -p 2di Q 2i Treat it as a virtual control input, denoted as Q. 2i Design control law α 2pi This makes the fifth tracking error z 5i =p 2i -p 2di It rapidly approaches zero;

[0152] Let α 2pi =α 2pai +α 2ps1i +α 2ps2i ,in α 2p =[α 2p1 α 2p2 α 2p3 ] T ,k p2i >0 represents the linear feedback gain; in this example, we take k. p21 =200,k p22 =100,k p23 =100; They are θ β θ Q2i The estimated value, θ p2i =[θ β θ Q2i ] T , It is θ p2i The estimated value, in this example, is taken as the initial value. And the range of the estimated values ​​is: in For parameter θ p2i The estimated value The minimum value, For parameter θ p2i The estimated value The maximum value; in this example, take make estimated value The lower-level pressure tracking controller is equipped with an adaptive rate. We get, Γ p2i It is a positive definite gain matrix. In this example, we take Γ. p2i =[0 0] T , The mapping function is:

[0153]

[0154] In the formula, · i The independent variable is the nonlinear robust feedback term α. 2ps2i The following two conditions must be met:

[0155]

[0156]

[0157] in, It is an estimated value. Subtract the actual value θ p2i , ε p2i It is a threshold and can be any non-negative number. In this embodiment, ε is selected. p2i =1, choose α 2ps2i =0.

[0158] (10) The expected flow rates of the rodless chambers of the ankle, knee, and hip hydraulic cylinders in the single-leg hydraulically assisted exoskeleton obtained in step (7) and the expected flow rates of the rod chambers of the ankle, knee, and hip hydraulic cylinders in the single-leg hydraulically assisted exoskeleton obtained in step (9) are used as the input quantities of the pump-valve flow distribution module. The output of the pump-valve flow distribution module is the control voltage of the electro-hydraulic servo valve of each hydraulic cylinder and the control voltage of the variable speed pump. The pump-valve flow distribution includes the following steps:

[0159] (10.1) Determine the control voltage u of the variable speed pump corresponding to hydraulic cylinder i. pi

[0160] if So sw 1i =1,sw 2i =0,

[0161] if So sw1i =0,sw 2i =1,

[0162] if So sw 1i =0,sw 2i =0, Q pdi =0;

[0163] in, Q represents the desired displacement of hydraulic cylinder i. pbound This represents the minimum boundary flow rate when using a variable speed pump; in this example, we take Q. pbound =1×10 -6 m 3 / s, Q pdi sw represents the expected output flow rate of the variable speed pump corresponding to hydraulic cylinder i. 1i and sw 2i These represent the on / off states of the switching valve when the flow rate from the pump control section in hydraulic cylinder i enters the rodless chamber and when it enters the rod chamber, respectively.

[0164] The control voltage of the variable speed pump corresponding to hydraulic cylinder i is Among them, the flow gain coefficient

[0165] (10.2) Determine the control voltage u of the servo valve corresponding to hydraulic cylinder i. pv1i u pv2i u pv3i u pv4i

[0166] Q 1pdi =sw 1i Q pdi Q 2pdi =sw 2i Q pdi Q 1vdi =Q 1mi -Q 1pdi Q 2vdi =α 2pi +Q 2pdi Q 1pdi and Q 2pdi Q represents the desired inlet flow rate of the rodless chamber and the desired inlet flow rate of the rod chamber from the pump control section in hydraulic cylinder i, respectively. 1vdi and Q 2vdi Q represents the desired inlet flow rate of the rodless chamber and the desired outlet flow rate of the rod chamber in hydraulic cylinder i, respectively, originating from the valve-controlled section. 1mi It is Q 1m The i-th element.

[0167] If Q 1vdi>0, then

[0168] If Q 1vdi <0, then

[0169] If Q 1vdi =0, then u pv1i =0, u pv3i =0;

[0170] If Q 2vdi >0, then

[0171] If Q 2vdi <0, then

[0172] If Q 2vdi =0, then u pv2i =0, u pv4i =0;

[0173] in, In summary, the control input signals for the pump control section and the valve control section can be obtained.

[0174] (11) The control voltage of the electro-hydraulic servo valve obtained in step (10) is converted into the control current of the corresponding servo valve through the amplification board of the ankle joint electro-hydraulic servo valve, the amplification board of the knee joint electro-hydraulic servo valve and the amplification board of the hip joint electro-hydraulic servo valve.

[0175] (12) The valve core opening displacement of the corresponding ankle joint valve control part servo valve 18, knee joint valve control part servo valve 20 and hip joint valve control part servo valve 22 is controlled by the control current of each servo valve. The speed of the servo motor of the corresponding ankle joint pump control part variable speed pump, knee joint pump control part variable speed pump and hip joint pump control part variable speed pump is controlled by the control voltage of each variable speed pump, so as to control the pressure at both ends of the hydraulic cylinder, drive each hydraulic cylinder to move, and then drive each joint of the single-leg hydraulic assist exoskeleton to rotate, so as to realize the following movement of the single-leg hydraulic assist exoskeleton.

[0176] In summary, in this embodiment, the single-leg hydraulically assisted exoskeleton control method of the present invention can be summarized into the following steps.

[0177] The first step involves using parallel pump-valve coordinated electro-hydraulic systems for the three hydraulic systems applied to the ankle, knee, and hip joints of the exoskeleton. Each parallel pump-valve coordinated electro-hydraulic system includes a parallel coordinated pump control section and a valve control section. The pump control section includes a variable pump control oil source PS1 and two two-way switching valves SV1 and SV2 that determine the direction of the outlet flow of the variable pump control oil source PS1. The valve control section includes four two-way electro-hydraulic servo valves PV1, PV2, PV3, and PV4 and a hydraulic oil source PS2. Electro-hydraulic servo valves PV1 and PV2 control the flow of hydraulic oil from the hydraulic oil source PS2 to the two chambers of the corresponding hydraulic cylinders, while electro-hydraulic servo valves PV3 and PV4 control the flow of hydraulic oil from the two chambers of the corresponding hydraulic cylinders to the oil tank.

[0178] This step requires installing three hydraulic systems on the exoskeleton for the ankle, knee, and hip joints.

[0179] The second step involves coordinating the parallel pump-valve electro-hydraulic system for each joint of the single-leg hydraulically assisted exoskeleton, based on the reference rotation angle of each joint. Reference rotational angular velocity Reference angular acceleration The actual driving force F of the hydraulic cylinder L Actual rotation angle q, actual rotation angular velocity The desired flow rate α of the rod cavity of each joint is obtained. 2p =[α 2p1 α 2p2 α 2p3 ] T And the expected flow rate Q of the rodless cavity 1m =[Q 1m1 Q 1m2 Q 1m3 ] T Where i represents the sequence number of the three joints, the expected flow rate of the rod cavity of the i-th joint is α. 2pi The expected flow rate of the rodless cavity of the i-th joint is Q. 1mi .

[0180] This step can be performed by the traffic acquisition module.

[0181] Among them, (1) The method for obtaining it includes the following steps:

[0182] According to the human-machine interaction force F hm Cartesian position x of the exoskeleton at the point of contact e Design an upper-level controller, wherein the upper-level controller is x. m =x ma +x ms +x msn Thus, the Cartesian expectation position x of the exoskeleton at the contact point is obtained. mIn the formula, x ma For x m The adaptive model compensation term, x ms For x m The linear robust feedback term, x msn For x m Nonlinear robust feedback term;

[0183] According to the design x m Based on the inverse kinematics model of a single-leg hydraulically assisted exoskeleton q m =invkine(x m Thus, the desired rotation angle q of each joint of the single-leg hydraulically assisted exoskeleton is obtained. m =[q m1 q m2 q m3 ] T q mi This represents the expected rotation angle of the i-th joint;

[0184] The desired rotation angle q of the i-th joint of a single-leg hydraulically assisted exoskeleton mi Let i = 1, 2, 3, and smooth the data using a fourth-order filter to obtain the reference rotation angle, reference rotation angular velocity, reference rotation angular acceleration, and reference rotation angular jerk of the i-th joint of the exoskeleton. The state equation of the fourth-order filter is as follows:

[0185]

[0186]

[0187]

[0188]

[0189] i = 1, 2, 3

[0190] In the formula, Represent the reference rotation angle, reference rotation angular velocity, reference rotation angular acceleration, and reference rotation angular jerk of the i-th joint of the filtered exoskeleton, respectively, from q mi To η 1i The transfer function is

[0191]

[0192] Using the transfer function described above, we obtain q. mi Transform into the reference rotation angle η of the i-th joint of the desired smooth exoskeleton. 1i The values ​​a1, a2, a3, and a4 in the transfer function are obtained through pole placement.

[0193] This provides the reference rotation angles for each joint of the single-leg hydraulically assisted exoskeleton. Reference rotational angular velocity Reference angular acceleration

[0194] (2) Expected flow rate Q of the rodless cavity of each joint of the single-leg hydraulically assisted exoskeleton 1m =[Q 1m1 Q 1m2 Q 1m3 ] T The calculation method includes the following steps:

[0195] according to q、 α 2p F L Design a rodless cavity position tracking controller, wherein the rodless cavity position tracking controller is Q 1m =Q 1ma +Q 1ms +Q 1msn Thus, the expected flow rate Q of the rodless cavity of each joint in the single-leg hydraulically assisted exoskeleton is obtained. 1m In the formula, Q 1ma For Q 1m The adaptive model compensation term, Q 1ms For Q 1m The linear robust feedback term, Q 1msn For Q 1m The nonlinear robust feedback term.

[0196] (3) Expected flow rate α of the rod-shaped cavity of each joint of the single-leg hydraulically assisted exoskeleton 2p =[α 2p1 α 2p2 α 2p3 ] T The calculation method includes the following steps:

[0197] according to q、 α 2p F L Design a rodless cavity position tracking controller, wherein the rodless cavity position tracking controller is F Ld =F Lda +F Lds +F Ldsn Thus, the desired driving force F of the hydraulic cylinders in each joint of the single-leg hydraulically assisted exoskeleton is obtained. Ld In the formula, F Lda For F Ld The adaptive model compensation term, F Lds For F Ld The linear robust feedback term, F Ldsn For F LdNonlinear robust feedback term;

[0198] According to F Ld =[F Ld1 F Ld2 F Ld3 ] T Design a rod-cavity pressure planner for each joint. Considering that a good control design can ensure that the system error is within a small range, an adaptive model compensation term F is used. Lda It can basically characterize the desired driving force F of the hydraulic cylinder. Ld In addition to the magnitude of the desired pressure in the rod cavity, to obtain a more continuous and smooth desired pressure and to avoid the negative impact of noise, a motion reference trajectory is used instead of the measured signal of the state quantity, i.e., the desired compensating driving force F of the hydraulic cylinder. Ldad =[F Ldad1 F Ldad2 F Ldad3 ] T The expected compensation driving force of the hydraulic cylinder of the i-th joint is F. Ldadi ;

[0199] For F at the i-th joint Ldadi The rod-cavity pressure planner for the i-th joint is This yields the expected pressure P in the rod cavity of the i-th joint. 2di In the formula, P c It is the set minimum working pressure, A 1i and A 2i Let represent the effective areas of the rodless cavity and the rod cavity in the i-th joint, respectively;

[0200] According to P 2di The actual pressure P in the rod cavity of the i-th joint 2i Design a rod-cavity pressure tracking controller for the i-th joint, wherein the rod-cavity pressure tracking controller for the i-th joint is α. 2pi =α 2pai +α 2ps1i +α 2ps2i Thus, the expected flow rate α of the rod cavity of the i-th joint is obtained. 2pi In the formula, α 2pai For α 2pi The adaptive model compensation term, α 2ps1i For α 2pi The linear robust feedback term, α 2ps2i For α 2pi Nonlinear robust feedback term;

[0201] This yields the expected flow rate α of the rod-shaped cavity in each joint of the single-leg hydraulically assisted exoskeleton. 2p =[α 2p1 α 2p2 α 2p3 ]T .

[0202] Third step, according to α 2p Q 1m Calculate the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint to distribute the pump and valve flow to each joint.

[0203] This step can be performed by the control voltage acquisition module. This solves the technical problems of high-order nonlinearity, model uncertainty, and high energy consumption in existing single-leg hydraulically assisted exoskeletons.

[0204] (1) The calculation method for the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint includes the following steps:

[0205] According to α 2p Q 1m Distribute pump and valve flow rates to each joint;

[0206] For the i-th joint, the control voltage u of the variable speed pump PS1 of the i-th joint is... pi for:

[0207] if So sw 1i =1,sw 2i =0,

[0208] if So sw 1i =0,sw 2i =1,

[0209] if So sw 1i =0,sw 2i =0, Q pdi =0;

[0210] in, Let Q represent the desired displacement of the hydraulic cylinder at the i-th joint. pbound Q represents the minimum boundary flow rate when using a variable speed pump. pdi sw represents the expected output flow rate of the variable speed pump at the i-th joint. 1i and sw 2i These represent the on / off states of the switching valve when the flow rate of the pump control section in the i-th joint enters the rodless chamber of the hydraulic cylinder and when it enters the rod chamber of the hydraulic cylinder, respectively.

[0211] The control voltage of the variable speed pump PS1 at the i-th joint is obtained as follows:

[0212] The control voltage u of the servo valve of the i-th joint pv1i u pv2i u pv3i u pv4i for:

[0213] Q 1pdi =sw 1i Q pdi Q 2pdi =sw 2i Q pdi Q 1vdi =Q 1mi -Q 1pdi Q 2vdi =α 2pi +Q 2pdi Q 1pdi and Q 2pdi Let Q represent the expected oil inlet flow rates of the rodless chamber and the rod chamber from the pump control section in the i-th joint, respectively. 1vdi and Q 2vdi Let them represent the expected inlet flow rate of the rodless chamber and the expected outlet flow rate of the rod chamber from the valve control section in the i-th joint, respectively.

[0214] If Q 1vdi >0, then

[0215] If Q 1vdi <0, then u pv1i =0,

[0216] If Q 1vdi =0, then u pv1i =0, u pv3i =0;

[0217] If Q 2vdi >0, then u pv2i =0,

[0218] If Q 2vdi <0, then

[0219] If Q 2vdi =0, then u pv2i =0, u pv4i =0;

[0220] Wherein, the control voltage of PV1 in the i-th joint is u pv1i The control voltage of PV2 in the i-th joint is u. pv2i The control voltage of PV3 in the i-th joint is u. pv3i The control voltage of PV4 in the i-th joint is u. pv4i;

[0221] This yields the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint.

[0222] Fourth step: Based on the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint, a dynamic model of the hydraulic actuator in the i-th joint is established. This yields the actual pressure P in the rod chamber corresponding to the hydraulic cylinder in the i-th joint. 2i In the formula, Q 2i x is the oil flow rate from the rod chamber of the hydraulic cylinder in the i-th joint; Li It is the displacement of the hydraulic cylinder in the i-th joint. It is x Li Regarding q i First-order partial derivative; V 2i =V h2i -A 2i x Li V is the total volume of the rod-side chamber of the hydraulic cylinder in the i-th joint. h2i It is q i When β = 0, the volume of the rod-side chamber of the hydraulic cylinder in the i-th joint, β e Indicates the bulk modulus of elasticity; This represents the lumped modeling error and uncertainties in the dynamic model of the hydraulic actuator in the i-th joint; from this, the actual pressure P2 of the rod-side chamber corresponding to the hydraulic cylinder in each joint of the single-leg hydraulically assisted exoskeleton is obtained; based on the actual pressure P of the rodless chamber corresponding to the hydraulic cylinder in the i-th joint... 1i And the actual pressure P in the rod chamber 2i The actual driving force F of the hydraulic cylinder in the i-th joint is obtained. Li =P 1i A 1i -P 2i A 2i Therefore, the actual driving force F of the hydraulic cylinders in each joint of the single-leg hydraulically assisted exoskeleton is obtained. L =[F L1 F L2 F L3 ] T .

[0223] This step can be performed by the module that obtains the actual driving force of the hydraulic cylinder.

[0224] The fifth step involves determining the actual driving force F of the hydraulic cylinders in each joint of the single-leg hydraulically assisted exoskeleton. L For the i-th joint, the actual driving torque τ of the i-th joint is thus obtained. i =F Li h i In the formula, h iThis represents the lever arm between the i-th joint rotation point and the hydraulic cylinder; thus, the actual joint driving torque τ of each joint of the single-leg hydraulically assisted exoskeleton is obtained. act =[τ1 τ2τ3] T .

[0225] This step can be performed by the module that obtains the actual driving torque of the joint.

[0226] Step 6, based on τ act And based on the motion model of the exoskeleton mechanical body This yields the actual rotation angle q and the actual rotational angular velocity of each joint. Where, τ act =[τ1 τ2 τ3] T Let M be the actual driving torque of the joints at the ankle, knee, and hip joints, J be the Jacobian matrix of the system at the force sensor, and M be the force of the system. sp3 (q) is the system's inertia matrix. It is the system's centrifugal force and Coriolis force matrix, G sp3 (q) is the gravity matrix of the system, and B = diag{B1,B2,B3} is the damping matrix of the system. It is a concentrated interference in the system.

[0227] This step can be performed by the rotational angular velocity acquisition module. Among them, steps four, five, and six describe the steps after the pump and valve flow distribution at each joint.

[0228] The single-leg hydraulic assistive exoskeleton control method of this invention employs a hydraulic system characterized by its small size, light weight, flexible layout, compact structure, ability to output significant force or torque, sensitive action response, and ease of control. The hydraulic system utilizes a parallel pump-valve coordinated electro-hydraulic system scheme, allowing the pump control section to provide the main flow and the valve control section to provide a minor flow, thus improving the energy efficiency of the lower limb assistive exoskeleton electro-hydraulic system. The single-leg hydraulic assistive exoskeleton control method of this invention employs a force control approach, utilizing an adaptive robust control algorithm (ARC) to design the upper and lower level controllers, effectively overcoming the influence of high-order nonlinearity and model uncertainty inherent in single-leg hydraulic assistive exoskeletons. In the lower level controller, the rodless chamber of the hydraulic cylinder employs position tracking control, while the rod chamber employs pressure tracking control, solving the technical problem of high energy consumption in existing exoskeleton control methods. This not only achieves excellent tracking and assistance of human movement with the hydraulic assistive exoskeleton but also reduces system energy consumption, achieving a longer operating time and demonstrating strong application value. This invention effectively overcomes the effects of strong multi-joint coupling, high-order nonlinearity of hydraulic actuators, and model uncertainty in single-leg hydraulically assisted exoskeletons. It not only achieves good tracking and assistance of human movement by hydraulically assisted exoskeletons, but also reduces system energy consumption and achieves a longer battery life.

[0229] In summary, compared with existing exoskeleton control methods, the single-leg hydraulically assisted exoskeleton control method and control device of the present invention, along with the exoskeleton itself, have the following beneficial effects:

[0230] 1. The single-leg hydraulically assisted exoskeleton control method uses a hydraulic drive system for its exoskeleton drive system, which has the characteristics of being able to output large force or torque, having sensitive action response, being easy to control, having small size, and having a compact structure.

[0231] 2. The control method for this single-leg hydraulic assistive exoskeleton adopts a parallel pump-valve coordinated electro-hydraulic system scheme, constructing an independently operating pump control part and valve control part, allowing the pump control part to provide the main flow and the valve control part to provide the minor flow, thereby improving the energy efficiency of the lower limb assistive exoskeleton electro-hydraulic system without sacrificing accuracy.

[0232] 3. The single-leg hydraulically assisted exoskeleton control method uses a sensor system consisting mainly of a back force sensor and a joint encoder to achieve reliable human-machine interaction.

[0233] 4. This single-leg hydraulically assisted exoskeleton control method employs a force control approach. An Adaptive Robust Control (ARC) algorithm is used to design the upper and lower level controllers, effectively overcoming the influence of high-order nonlinearity and model uncertainty inherent in single-leg hydraulically assisted exoskeletons. In the lower level controller, the rodless chamber of the hydraulic cylinder uses position tracking control, while the rod chamber uses pressure tracking control, ensuring that the pressure in one chamber of the hydraulic cylinder is always at its minimum. This solves the technical problem of high energy consumption in existing exoskeleton control methods. It not only achieves excellent tracking and assistance of human movement with the hydraulically assisted exoskeleton but also reduces system energy consumption and achieves a longer operating time, demonstrating strong application value.

[0234] 5. This single-leg hydraulically assisted exoskeleton control method uses human movement as the external input for the entire exoskeleton system, ensuring balance during walking. Furthermore, it employs a cascaded force control algorithm to enable the exoskeleton to follow the human's trajectory. The control method is simple to implement, easy to engineer, and offers flexible control.

[0235] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling a single-leg hydraulically assisted exoskeleton, used to control the movement of a single-leg hydraulically assisted exoskeleton; characterized in that, The control method includes the following steps: The three hydraulic systems applied to the ankle, knee, and hip joints of the exoskeleton respectively all adopt parallel pump-valve coordinated electro-hydraulic systems. Each parallel pump-valve coordinated electro-hydraulic system includes a parallel coordinated pump control part and a valve control part. The pump control part includes a variable pump control oil source PS1 and two two-way switching valves SV1 and SV2 that determine the direction of the outlet flow of the variable pump control oil source PS1. The valve control part includes four two-way electro-hydraulic servo valves PV1, PV2, PV3, and PV4 and a hydraulic oil source PS2. The electro-hydraulic servo valves PV1 and PV2 control the flow of hydraulic oil source PS2 to the two chambers of the corresponding hydraulic cylinders, and the electro-hydraulic servo valves PV3 and PV4 control the flow of hydraulic oil from the two chambers of the corresponding hydraulic cylinders to the oil tank. For the parallel pump-valve coordinated electro-hydraulic system of each joint in a single-leg hydraulically assisted exoskeleton, based on the reference rotation angle of each joint... Reference rotational angular velocity Reference angular acceleration The actual driving force F of the hydraulic cylinder L Actual rotation angle q, actual rotation angular velocity The desired flow rate α of the rod cavity of each joint is obtained. 2p =[α 2p1 α 2p2 α 2p3 ] T And the expected flow rate Q of the rodless cavity 1m =[Q 1m1 Q 1m2 Q 1m3 ] T Where i represents the sequence number of the three joints, the expected flow rate of the rod cavity of the i-th joint is α. 2pi The expected flow rate of the rodless cavity of the i-th joint is Q. 1mi ; According to α 2p Q 1m Calculate the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint in order to distribute the pump and valve flow to each joint. The calculation method for the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint includes the following steps: According to α 2p Q 1m Distribute pump and valve flow rates to each joint; For the i-th joint, the control voltage u of the variable speed pump PS1 of the i-th joint is... pi for: if So sw 1i =1,sw 2i =0, if So sw 1i =0,sw 2i =1, if So sw 1i =0,sw 2i =0, Q pdi =0; in, Let Q represent the desired displacement of the hydraulic cylinder at the i-th joint. pbound Q represents the minimum boundary flow rate when using a variable speed pump. pdi sw represents the expected output flow rate of the variable speed pump at the i-th joint. 1i and sw 2i These represent the on / off states of the switching valve when the flow rate of the pump control section in the i-th joint enters the rodless chamber of the hydraulic cylinder and when it enters the rod chamber of the hydraulic cylinder, respectively. The control voltage of the variable speed pump PS1 at the i-th joint is obtained as follows: The control voltage u of the servo valve of the i-th joint pv1i u pv2i u pv3i u pv4i for: Q 1pdi =sw 1i Q pdi Q 2pdi =sw 2i Q pdi Q 1vdi =Q 1mi -Q 1pdi Q 2vdi =α 2pi +Q 2pdi Q 1pdi and Q 2pdi Let Q represent the expected oil inlet flow rates of the rodless chamber and the rod chamber from the pump control section in the i-th joint, respectively. 1vdi and Q 2vdi Let them represent the expected inlet flow rate of the rodless chamber and the expected outlet flow rate of the rod chamber from the valve control section in the i-th joint, respectively. If Q 1vdi >0, then u pv3i =0; If Q 1vdi <0, then u pv1i =0, If Q 1vdi =0, then u pv1i =0, u pv3i =0; If Q 2vdi >0, then u pv2i =0, If Q 2vdi <0, then If Q 2vdi =0, then u pv2i =0, u pv4i =0; Wherein, the control voltage of PV1 in the i-th joint is u pv1i The control voltage of PV2 in the i-th joint is u. pv2i The control voltage of PV3 in the i-th joint is u. pv3i The control voltage of PV4 in the i-th joint is u. pv4i ; This yields the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint.

2. The single-leg hydraulically assisted exoskeleton control method as described in claim 1, characterized in that, Desired flow rate Q in the rodless cavity of each joint of a single-leg hydraulically assisted exoskeleton 1m =[Q 1m1 Q 1m2 Q 1m3 ] T The calculation method includes the following steps: according to q、 α 2p F L Design a rodless cavity position tracking controller, wherein the rodless cavity position tracking controller is Q 1m =Q 1ma +Q 1ms +Q 1msn Thus, the expected flow rate Q of the rodless cavity of each joint in the single-leg hydraulically assisted exoskeleton is obtained. 1m In the formula, Q 1ma For Q 1m The adaptive model compensation term, Q 1ms For Q 1m The linear robust feedback term, Q 1msn For Q 1m The nonlinear robust feedback term.

3. The single-leg hydraulically assisted exoskeleton control method as described in claim 1, characterized in that, Desired flow rate α in the rod-shaped cavities of each joint of a single-leg hydraulically assisted exoskeleton 2p =[α 2p1 α 2p2 α 2p3 ] T The calculation method includes the following steps: according to q、 α 2p F L Design a rodless cavity position tracking controller, wherein the rodless cavity position tracking controller is F Ld =F Lda +F Lds +F Ldsn Thus, the desired driving force F of the hydraulic cylinders in each joint of the single-leg hydraulically assisted exoskeleton is obtained. Ld In the formula, F Lda For F Ld The adaptive model compensation term, F Lds For F Ld The linear robust feedback term, F Ldsn For F Ld Nonlinear robust feedback term; According to F Ld =[F Ld1 F Ld2 F Ld3 ] T Design a rod-cavity pressure planner for each joint, using a motion reference trajectory instead of the measured signals of the state variables, i.e., the desired compensating driving force F of the hydraulic cylinder. Ldad =[F Ldad1 F Ldad2 F Ldad3 ] T The expected compensation driving force of the hydraulic cylinder of the i-th joint is F. Ldadi ; For F at the i-th joint Ldadi The rod-cavity pressure planner for the i-th joint is This yields the expected pressure P in the rod cavity of the i-th joint. 2di In the formula, P c It is the set minimum working pressure, A 1i and A 2i Let represent the effective areas of the rodless cavity and the rod cavity in the i-th joint, respectively; According to P 2di The actual pressure P in the rod cavity of the i-th joint 2i Design a rod-cavity pressure tracking controller for the i-th joint, wherein the rod-cavity pressure tracking controller for the i-th joint is α. 2pi =α 2pai +α 2ps1i +α 2ps2i Thus, the expected flow rate α of the rod cavity of the i-th joint is obtained. 2pi In the formula, α 2pai For α 2pi The adaptive model compensation term, α 2ps1i For α 2pi The linear robust feedback term, α 2ps2i For α 2pi Nonlinear robust feedback term; This yields the expected flow rate α of the rod-shaped cavity in each joint of the single-leg hydraulically assisted exoskeleton. 2p =[α 2p1 α 2p2 α 2p3 ] T .

4. The single-leg hydraulically assisted exoskeleton control method as described in claim 1, characterized in that, The single-leg hydraulically assisted exoskeleton control method also includes the following steps: Based on the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint, the dynamic model of the hydraulic actuator in the i-th joint is established. This yields the actual pressure P in the rod chamber corresponding to the hydraulic cylinder in the i-th joint. 2i In the formula, Q 2i x is the oil flow rate from the rod chamber of the hydraulic cylinder in the i-th joint; Li It is the displacement of the hydraulic cylinder in the i-th joint. It is x Li Regarding q i First-order partial derivative; V 2i =V h2i -A 2i x Li V is the total volume of the rod-side chamber of the hydraulic cylinder in the i-th joint. h2i It is q i When β = 0, the volume of the rod-side chamber of the hydraulic cylinder in the i-th joint, β e Indicates the bulk modulus of elasticity; This represents the concentrated modeling error and uncertain disturbance in the dynamic model of the hydraulic actuator in the i-th joint; thus, the actual pressure P2 of the rod chamber corresponding to the hydraulic cylinder in each joint of the single-leg hydraulically assisted exoskeleton is obtained. Based on the actual pressure P of the rodless chamber corresponding to the hydraulic cylinder in the i-th joint 1i And the actual pressure P in the rod chamber 2i The actual driving force F of the hydraulic cylinder in the i-th joint is obtained. Li =P 1i A 1i -P 2i A 2i Therefore, the actual driving force F of the hydraulic cylinders in each joint of the single-leg hydraulically assisted exoskeleton is obtained. L =[F L1 F L2 F L3 ] T .

5. The single-leg hydraulically assisted exoskeleton control method as described in claim 4, characterized in that, The single-leg hydraulically assisted exoskeleton control method also includes the following steps: Based on the actual driving force F of the hydraulic cylinders in each joint of the single-leg hydraulically assisted exoskeleton L For the i-th joint, the actual driving torque τ of the i-th joint is thus obtained. i =F Li h i In the formula, h i This represents the lever arm between the i-th joint rotation point and the hydraulic cylinder; thus, the actual joint driving torque τ of each joint of the single-leg hydraulically assisted exoskeleton is obtained. act =[τ1τ2τ3] T .

6. The single-leg hydraulically assisted exoskeleton control method as described in claim 4, characterized in that, The single-leg hydraulically assisted exoskeleton control method also includes the following steps: According to τ act And based on the motion model of the exoskeleton mechanical body This yields the actual rotation angle q and the actual rotational angular velocity of each joint. Where, τ act =[τ1τ2τ3] T Let M be the actual driving torque of the joints at the ankle, knee, and hip joints, J be the Jacobian matrix of the system at the back force sensor (24) used to measure human-machine interaction forces, and M be the actual driving torque of the joints at the ankle, knee, and hip joints. sp3 (q) is the system's inertia matrix. It is the system's centrifugal force and Coriolis force matrix, G sp3 (q) is the gravity matrix of the system, and B = diag{B1,B2,B3} is the damping matrix of the system. It is a concentrated interference in the system.

7. The single-leg hydraulically assisted exoskeleton control method as described in claim 1, characterized in that, The method for obtaining it includes the following steps: According to the human-machine interaction force F hm Cartesian position x of the exoskeleton at the point of contact e Design an upper-level controller, wherein the upper-level controller is x. m =x ma +x ms +x msn Thus, the Cartesian expectation position x of the exoskeleton at the contact point is obtained. m In the formula, x ma For x m The adaptive model compensation term, x ms For x m The linear robust feedback term, x msn For x m Nonlinear robust feedback term; According to the design x m Based on the inverse kinematics model of a single-leg hydraulically assisted exoskeleton q m =invkine(x m Thus, the desired rotation angle q of each joint of the single-leg hydraulically assisted exoskeleton is obtained. m =[q m1 q m2 q m3 ] T q mi This represents the expected rotation angle of the i-th joint; The desired rotation angle q of the i-th joint of a single-leg hydraulically assisted exoskeleton mi Let i = 1, 2, 3, and smooth the data using a fourth-order filter to obtain the reference rotation angle, reference rotation angular velocity, reference rotation angular acceleration, and reference rotation angular jerk of the i-th joint of the exoskeleton. The state equation of the fourth-order filter is as follows: i＝1,2,3 In the formula, Represent the reference rotation angle, reference rotation angular velocity, reference rotation angular acceleration, and reference rotation angular jerk of the i-th joint of the filtered exoskeleton, respectively, from q mi To η 1i The transfer function is Using the transfer function described above, we obtain q. mi Transform into the reference rotation angle η of the i-th joint of the desired smooth exoskeleton. 1i The values ​​a1, a2, a3, and a4 in the transfer function are obtained through pole placement. This provides the reference rotation angles for each joint of the single-leg hydraulically assisted exoskeleton. Reference rotational angular velocity Reference angular acceleration 8. A single-leg hydraulically assisted exoskeleton, characterized in that, It employs the single-leg hydraulically assisted exoskeleton control method as described in any one of claims 1 to 7.

9. A single-leg hydraulically assisted exoskeleton control device, which employs the single-leg hydraulically assisted exoskeleton control method as described in any one of claims 1 to 7, characterized in that, The control device includes: The flow acquisition module is used to coordinate the electro-hydraulic system with parallel pumps and valves for each joint of the single-leg hydraulically assisted exoskeleton, based on the reference rotation angle of each joint. Reference rotational angular velocity Reference angular acceleration The actual driving force F of the hydraulic cylinder L Actual rotation angle q, actual rotation angular velocity The desired flow rate α of the rod cavity of each joint is obtained. 2p =[α 2p1 α 2p2 α 2p3 ] T And the expected flow rate Q of the rodless cavity 1m =[Q 1m1 Q 1m2 Q 1m3 ] T Where i represents the sequence number of the three joints, the expected flow rate of the rod cavity of the i-th joint is α. 2pi The expected flow rate of the rodless cavity of the i-th joint is Q. 1mi ; The control voltage acquisition module is used to determine the voltage based on α. 2p Q 1m Calculate the control voltages PS1, PV1, PV2, PV3, and PV4 corresponding to each joint in order to distribute the pump and valve flow to each joint. Each parallel pump-valve coordinated electro-hydraulic system includes a parallel coordinated pump control section and a valve control section. The pump control section includes a variable pump control oil source PS1 and two two-way switching valves SV1 and SV2 that determine the direction of the outlet flow of the variable pump control oil source PS1. The valve control section includes four two-way electro-hydraulic servo valves PV1, PV2, PV3 and PV4 and a hydraulic oil source PS2. The electro-hydraulic servo valves PV1 and PV2 control the flow of hydraulic oil source PS2 to the two chambers of the corresponding hydraulic cylinder, and the electro-hydraulic servo valves PV3 and PV4 control the flow of hydraulic oil from the two chambers of the corresponding hydraulic cylinder to the oil tank.

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