Three-degree-of-freedom redundant parallel mechanism suitable for wave compensation ship and compensation method of three-degree-of-freedom redundant parallel mechanism

Abstract

The invention relates to a three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship and a compensation method thereof.The three-degree-of-freedom redundant parallel mechanism comprises a lower deck and an upper deck, the lower deck and the upper deck are arranged in parallel, a plurality of wave compensation branch chains are connected between the lower deck and the upper deck, and the wave compensation branch chains comprise redundant branch chains and non-redundant branch chains; the redundant branch chains and the non-redundant branch chains located in the same row or the same column are arranged in a crossed mode, the non-redundant branch chains comprise the first non-redundant branch chain and the second non-redundant branch chain, the non-redundant branch chains are arranged in an isosceles triangle mode with the second non-redundant branch chain as the vertex, and the rest of the non-redundant branch chains are the redundant branch chains. The position precision of the mechanism is guaranteed through the position control branch chains, time-varying nonlinear motion in the heaving, rolling and pitching directions is dynamically compensated in real time, meanwhile, the redundant structural force control branch chains balance driving force of all the branch chains by adjusting the driving force, the bearing capacity of the mechanism can be improved, and good overall rigidity is achieved.

Description

Technical Field

[0001] The present invention relates to a redundant parallel mechanism and a compensation method thereof, and particularly to a three-degree-of-freedom redundant parallel mechanism applicable to a wave compensation ship and a compensation method thereof. Background Art

[0002] Ships and offshore operation platforms often experience significant heaving motions under the action of waves. Yawing, swaying, and surging among the six degrees of freedom mainly affect the trajectory of the ship, while heaving, rolling, and pitching affect the attitude of the ship, and the motion amplitudes are relatively large, thus having a significant impact on the operations of the staff and construction machinery.

[0003] Existing wave compensation platforms have problems such as low stiffness and poor load-bearing capacity, and cannot achieve complete compensation for the position and attitude of the stable platform, and are more unsuitable for heavy-load-bearing occasions. Therefore, compensating for the three degrees of freedom of heaving, rolling, and pitching of ships and offshore operation platforms and improving the load-bearing capacity of the wave compensation platform have become technical problems that need to be solved urgently at present.

[0004] The invention patent of CN109625177A discloses a three-degree-of-freedom wave compensation platform, which realizes three-degree-of-freedom wave compensation through three groups of lifting mechanisms. In order to accelerate the compensation response speed, the stiffness of this platform is reduced, resulting in poor load-bearing capacity of the platform; the invention patent of CN202211373810.2 discloses a three-degree-of-freedom wave compensation platform, which adopts a plurality of servo electric cylinders and a complex mechanical structure. Although wave compensation can be effectively realized, the complexity of this structure leads to increased manufacturing, maintenance, and operation difficulties, increases the production and use costs, the platform design is huge and complex, resulting in a large self-weight, affecting the overall stability, and having insufficient load-bearing capacity. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to propose a three-degree-of-freedom redundant parallel mechanism applicable to a wave compensation ship and a compensation method thereof, so as to perform real-time dynamic compensation for the time-varying nonlinear motions of a ship or an offshore operation platform in the heaving, rolling, and pitching directions under the action of sea waves, and improve the load-bearing capacity of the wave compensation platform, providing a stable working platform for offshore engineering operations.

[0006] Technical Solution: The present invention includes a lower deck and an upper deck, and a plurality of wave compensation chains are connected between the lower deck and the upper deck. The wave compensation chains include redundant chains and non-redundant chains. The redundant chains and non-redundant chains in the same row or the same column are arranged crosswise respectively. The non-redundant chains include a first non-redundant chain and a second non-redundant chain. The non-redundant chains are arranged in an isosceles triangle with the second non-redundant chain as the vertex, and the rest are redundant chains.

[0007] The redundant and non-redundant branches in the same row are arranged on the same straight line, and the redundant and non-redundant branches in the same column are arranged on the same straight line. The central points of the universal hinges where each branch is connected to the upper deck form a rectangular structure, and the central points of the connectors where each branch is connected to the lower deck also form a rectangular structure.

[0008] The non-redundant branches adopt a position control mode, and the redundant branches adopt a force following control method. The non-redundant branches, as the redundant driving branches of the parallel mechanism, can improve the system stiffness, enhance the dynamic performance of the platform and improve the motion accuracy of the platform with the driving force generated.

[0009] The hydraulic cylinders or electric cylinders used for the non-redundant branches are active cylinders, and the hydraulic cylinders or electric cylinders used for the redundant branches are passive cylinders. Position sensors are installed on both the active cylinders and the passive cylinders. When arranging the positions of the actuators, the local design of each installation position of the hydraulic cylinders or electric cylinders should meet the requirements of being in the same plane, high position accuracy, etc., to ensure and improve the control accuracy of the active wave compensation system. At the initial position, the extension lengths of the six hydraulic cylinders or electric cylinders should be equal.

[0010] A first attitude sensor is installed at the center of gravity position of the upper deck, and a second attitude sensor is installed on the lower deck. Both the first attitude sensor and the second attitude sensor are connected to the motion controller.

[0011] The lower deck and the upper deck are arranged in parallel.

[0012] The first non-redundant branch includes a cylinder block. A force sensor is provided at the end of the push rod of the cylinder block. The other end of the force sensor is connected to a universal joint, and the universal joint is connected to the upper deck. The bottom of the cylinder block is connected to the lower deck through a hinge.

[0013] The second non-redundant branch includes a cylinder block. A force sensor is provided at the end of the push rod of the cylinder block. The other end of the force sensor is connected to a universal joint through a rotating bearing, and the universal joint is connected to the upper deck. The bottom of the cylinder block is connected to the lower deck through a hinge.

[0014] The redundant branch includes a cylinder block. A force sensor is provided at the end of the push rod of the cylinder block. The other end of the force sensor is connected to a universal joint through a rotating bearing, and the universal joint is connected to the upper deck. The bottom of the cylinder block is connected to a universal joint through a rotating bearing, and the universal joint is connected to the lower deck.

[0015] A compensation method for a three-degree-of-freedom redundant parallel mechanism applicable to a wave compensation ship includes the following steps:

[0016] S1. Measure the motion attitude values of the roll, pitch, and heave of the hull through the second attitude sensor on the lower deck, and then plan the trajectory of the upper deck in combination with the actual attitude and the target attitude of the upper deck;

[0017] S2. The non-redundant branch chain controls the movement of the branch chain according to the trajectory planning result of S1. The specific motion control strategy is as follows: decompose the trajectory planning result into each branch chain to obtain the planned rod lengths of each branch chain; compare the real-time measurement data of the position sensors of each branch chain with the planned rod lengths to obtain a position difference signal; use the force measured by the force sensor as a feedforward signal; input the difference signal and the feedforward signal into the PID controller to perform closed-loop control on the position control branch chain.

[0018] S3. The redundant branch chain adopts a force control mode. The controller records the measured value of the force sensor when the mechanism is stable as a preset value. When the wave compensation function is started, the force control branch chain compares the real-time force value with the preset value to obtain a force difference signal, and inputs the difference signal into the PID controller to perform closed-loop control on the force control branch chain.

[0019] S4. Measure the actual attitude of the upper deck through the first attitude sensor on the upper deck, substitute the actual attitude into S1, and repeat S1 - S4.

[0020] Beneficial effects: The present invention ensures the position accuracy of the mechanism through the position control branch chain, performs real-time dynamic compensation on the time-varying non-linear motions in the heave, roll, and pitch directions. At the same time, the redundant structure force control branch chain can improve the bearing capacity and overall stiffness of the mechanism by adjusting the driving force to balance the driving forces of all branch chains. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0022] Figure 2 It is a schematic diagram of the non-redundant branch chain RPU structure of the present invention;

[0023] Figure 3 It is a schematic diagram of the non-redundant branch chain RCU structure of the present invention;

[0024] Figure 4 It is a schematic diagram of the redundant branch chain UCU structure of the present invention;

[0025] Figure 5 It is a flowchart of the present invention. Detailed Embodiments

[0026] The present invention will be further described below with reference to the drawings.

[0027] Embodiment 1

[0028] As Figure 1As shown in the figure, the three-degree-of-freedom redundant parallel mechanism applicable to wave compensation vessels in this embodiment includes a lower deck 7 and an upper deck 8. The lower deck 7 is installed on a ship or an offshore operation platform and serves as the installation base for mounting the three-degree-of-freedom wave compensation platform onto the ship or the offshore operation platform. The upper deck 8 is used to install attitude sensors and construction machinery or offshore operation platforms. The lower deck 7 and the upper deck 8 are arranged in parallel, and a plurality of wave compensation chains are connected between the lower deck 7 and the upper deck 8. The wave compensation chains include redundant chains 2 and non-redundant chains. The redundant chains 2 can improve the load-bearing capacity of the mechanism to ensure the overall load safety of the active wave compensation chains. The redundant chains 2 and the non-redundant chains located in the same row or the same column are arranged crosswise respectively. Among them, at least three non-redundant chains are provided. The non-redundant chains include a first non-redundant chain 1 and a second non-redundant chain 3. In this embodiment, three non-redundant chains are provided, namely two first non-redundant chains 1 and one second non-redundant chain 3. The three non-redundant chains are arranged in an isosceles triangle with the second non-redundant chain 3 as the vertex. The remaining are three redundant chains 2, and the three redundant chains 2 are also arranged in an isosceles triangle.

[0029] The redundant chains 2 and the non-redundant chains located in the same row are arranged on the same straight line, and the redundant chains 2 and the non-redundant chains located in the same column are also arranged on the same straight line. The center points of the universal hinges where each chain is connected to the upper deck form a rectangular structure, and the center points of the connectors where each chain is connected to the lower deck also form a rectangular structure. The hydraulic cylinders or electric cylinders used in the non-redundant chains are active cylinders, and the hydraulic cylinders or electric cylinders used in the redundant chains are passive cylinders. When the mechanism performs motion compensation, the hydraulic cylinders or electric cylinders of the three non-redundant chains actively expand and contract for wave compensation, and the hydraulic cylinders or electric cylinders of the three redundant chains passively expand and contract. Position sensors are installed on each active cylinder and passive cylinder to measure the displacement of the actuator's telescopic motion. Force sensors are installed at the ends of the push rods of the active cylinders and passive cylinders to collect the force exerted by the upper deck 8 on the chains in real time. The hydraulic cylinders or electric cylinders compensate for the roll, pitch, and heave of the upper deck 8 through expansion and contraction.

[0030] When arranging the positions of the actuators, the local design of the installation positions of the hydraulic cylinders or electric cylinders should meet the requirements of being in the same plane, high position accuracy, etc., which can ensure and improve the control accuracy of the active wave compensation system. At the initial position, the extension amounts of the six hydraulic cylinders or electric cylinders should be equal.

[0031] A first attitude sensor 9 is installed at the center of gravity position of the upper deck 8. The first attitude sensor 9 is connected to the motion controller through a signal line. The first attitude sensor 9 is used to detect the motion attitude values of the roll, pitch, and heave of the upper deck 8, and input the detected values into the motion controller. A second attitude sensor 10 is installed on the lower deck 7. The second attitude sensor 10 is connected to the motion controller through a signal line and is used to measure the actual rotation angle. The motion controller calculates the compensation values of roll, pitch, and heave according to the inverse solution algorithm of the wave compensation value, and controls the actions of each actuator, namely the hydraulic cylinder or the electric cylinder, according to the compensation values to achieve the three-degree-of-freedom compensation of the upper deck 8.

[0032] The non-redundant branch chain adopts a position control mode to ensure the end accuracy of wave compensation through a three-point positioning method; in order to control the redundant internal stress generated during the motion state of the mechanism, a force following control method is adopted for the redundant branch chain 2. The non-redundant branch chain, as the redundant drive branch chain of the parallel mechanism, the driving force generated by it can improve the stiffness of the system, enhance the dynamic performance of the platform and improve the motion accuracy of the platform. When the system starts the wave compensation function, the controller performs kinematic and dynamic calculations based on the set target attitude of the upper deck 8 and the data measured by the sensors, and then performs motion planning for each branch chain according to the calculation results.

[0033] As Figure 2 shown, the first non-redundant branch chain 1 is an RPU branch chain, including a cylinder block 14. The cylinder block 14 adopts a hydraulic cylinder or an electric cylinder. A force sensor 13 is provided at the end of the push rod of the cylinder block 14. The other end of the force sensor 13 is connected to a universal joint 11 through a flange. The universal joint 11 is connected to the upper deck 8 through a backing plate. The bottom of the cylinder block 14 is connected to the lower deck 7 through a hinge 15. A backing plate is provided between the hinge 15 and the lower deck 7. The function of the backing plate in the mechanism is to make the bottoms of the six hydraulic cylinders or electric cylinders be in the same plane, and at the initial position, the elongation amounts of the six hydraulic cylinders or electric cylinders are the same.

[0034] As Figure 3 shown, the second non-redundant branch chain 3 is an RCU branch chain, including a cylinder block 14. The cylinder block 14 adopts a hydraulic cylinder or an electric cylinder. A force sensor 13 is provided at the end of the push rod of the cylinder block 14. The other end of the force sensor 13 is connected to a universal joint 11 through a rotating bearing 12. The universal joint 11 is connected to the upper deck 8 through a backing plate. The bottom of the cylinder block 14 is connected to the lower deck 7 through a hinge 15. A backing plate is provided between the hinge 15 and the lower deck 7. The function of the backing plate in the mechanism is to make the bottoms of the six hydraulic cylinders or electric cylinders be in the same plane, and at the initial position, the elongation amounts of the six hydraulic cylinders or electric cylinders are the same.

[0035] As Figure 4As shown in the figure, the redundant branch chain 2 is a UCU branch chain, including a cylinder block 14. The cylinder block 14 uses a hydraulic cylinder or an electric cylinder. A force sensor 13 is provided at the end of the push rod of the cylinder block 14. The other end of the force sensor 13 is connected to a universal joint 11 through a rotating bearing 12. The universal joint 11 is connected to the upper deck 8 through a backing plate. The bottom of the cylinder block 14 is connected to the universal joint 11 through a rotating bearing 12. The universal joint 11 is connected to the lower deck 7. A backing plate is provided between the universal joint 11 and the lower deck 7. The function of the backing plate in the mechanism is to make the bottoms of the six hydraulic cylinders or electric cylinders be in the same plane, and when in the initial position, the elongation amounts of the six hydraulic cylinders or electric cylinders are the same.

[0036] Embodiment 2

[0037] As Figure 5 shown, the compensation method of the three-degree-of-freedom redundant parallel mechanism applicable to a wave compensation ship in this embodiment includes the following steps:

[0038] S1. Measure the motion attitude values of the roll, pitch, and heave of the hull through the second attitude sensor 10 on the lower deck, and then combine the actual attitude and the target attitude (which can be 0 degrees or a certain specific angle) of the upper deck to plan the trajectory of the upper deck.

[0039] S2. According to the trajectory planning result of S1, the non-redundant branch chain controls the motion of the branch chain. The specific motion control strategy is: decompose the trajectory planning result into each branch chain to obtain the planned rod lengths of each branch chain; compare the real-time measurement data of the position sensors of each branch chain with the planned rod lengths to obtain the position difference signal; use the force measured by the force sensor as the feedforward signal; input the difference signal and the feedforward signal into the PID controller to perform closed-loop control on the position control branch chain.

[0040] S3. The redundant branch chain adopts a force control mode. The controller records the measurement value of the force sensor when the mechanism is stable as the preset value. When the wave compensation function is started, the force control branch chain compares the real-time force value with the preset value to obtain the force difference signal, and inputs the difference signal into the PID controller to perform closed-loop control on the force control branch chain to ensure that the internal stress at the connection between the corresponding branch chain and the upper upper deck is small, so that the corresponding branch chain can play a supporting role without being deformed by internal forces.

[0041] S4. Measure the actual attitude of the upper deck through the first attitude sensor on the upper deck, substitute the actual attitude into S1, and repeat S1 - S4.

[0042] The present invention can achieve the compensation of time-varying non-linear motions in the heave, roll and pitch directions, as well as the superimposed motion in the three directions. The three-degree-of-freedom redundant parallel mechanism balances the driving forces of each branch chain, improves the driving ability of the system. In the entire control system, the position control branch chain ensures the position accuracy of the mechanism, while the force control branch chain adjusts the driving force to balance the driving forces of all branch chains, enabling the mechanism to have a high overall stiffness and good motion performance. The three-degree-of-freedom redundant parallel mechanism can overcome complex relative motions such as heave, surge and roll generated by waves, improve the bearing capacity, and achieve the wave compensation function that meets the requirements.

Claims

1. A three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship, characterized in that: It includes a lower deck and an upper deck, and a plurality of wave compensation branches are connected between the lower deck and the upper deck. The wave compensation branches include redundant branches and non-redundant branches. The redundant branches and non-redundant branches located in the same row or column are cross-arranged respectively. The non-redundant branches include a first non-redundant branch and a second non-redundant branch. The non-redundant branches are arranged in an isosceles triangle with the second non-redundant branch as the vertex, and the rest are redundant branches.

2. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 1, characterized in that: The non-redundant branch chain adopts a position control mode, and the redundant branch chain adopts a force following control mode.

3. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 1, characterized in that: The redundant branches and non-redundant branches in the same row are arranged on the same straight line, and the redundant branches and non-redundant branches in the same column are arranged on the same straight line.

4. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 2, characterized in that: The hydraulic cylinder or electric cylinder used in the non-redundant branch chain is an active cylinder, and the hydraulic cylinder or electric cylinder used in the redundant branch chain is a passive cylinder. Position sensors are installed on both the active cylinder and the passive cylinder.

5. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 1, characterized in that: A first attitude sensor is installed at the center of gravity of the upper deck, and a second attitude sensor is installed on the lower deck. Both the first attitude sensor and the second attitude sensor are connected to the motion controller.

6. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 5, characterized in that: The lower deck and the upper deck are arranged in parallel.

7. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 1, characterized in that: The first non-redundant branch chain includes a cylinder body, a force sensor is provided at the end of the push rod of the cylinder body, the other end of the force sensor is connected to the universal joint, the universal joint is connected to the upper deck, and the bottom of the cylinder body is connected to the lower deck through a hinge.

8. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 1, characterized in that: The second non-redundant branch chain includes a cylinder body, a force sensor is provided at the end of the push rod of the cylinder body, the other end of the force sensor is connected to the universal joint through a rotating bearing, the universal joint is connected to the upper deck, and the bottom of the cylinder body is connected to the lower deck through a hinge.

9. The three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship according to claim 1, characterized in that: The redundant branch chain includes a cylinder body, a force sensor is provided at the end of the push rod of the cylinder body, the other end of the force sensor is connected to the universal joint through a rotating bearing, the universal joint is connected to the upper deck, the bottom of the cylinder body is connected to the universal joint through a rotating bearing, and the universal joint is connected to the lower deck.

10. A compensation method for a three-degree-of-freedom redundant parallel mechanism suitable for a wave compensation ship, characterized in that: The following steps are involved: S1. The second attitude sensor on the lower deck measures the rolling, pitching and heaving motion attitude values ​​of the ship, and then plans the trajectory of the upper deck in combination with the actual attitude and target attitude of the upper deck; S2, the non-redundant branch chain controls the movement of the branch chain according to the trajectory planning result of S1. The specific motion control strategy is: decompose the trajectory planning result into each branch chain to obtain the planned rod length of each branch chain; compare the real-time measurement data of the position sensor of each branch chain with the planned rod length to obtain the position difference signal; use the force measured by the force sensor as the feedforward signal; transmit the difference signal and the feedforward signal to the PID controller to perform closed-loop control on the position control branch chain; S3, the redundant branch chain adopts the force control mode. The controller records the measured value of the force sensor when the mechanism is stable, which is the preset value. When the wave compensation function is started, the force control branch chain compares the real-time force value with the preset value to obtain the force difference signal, and transmits the difference signal to the PID controller to perform closed-loop control on the force control branch chain; S4. Measure the actual posture of the upper deck through the first posture sensor on the upper deck, substitute the actual posture into S1, and repeat S1 to S4.

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