APPLICATIONS AND CHALLENGES FOR UNDERWATER SWIMMING MANIPULATORS Jørgen Sverdrup-Thygeson AMOS Days October 2017
Introduction
NEEDS FOR SUBSEA INSPECTION, MAINTENANCE AND REPAIR The number of new subsea installations are increasing. An ageing subsea infrastructure. More complex structures are deployed subsea and at greater depths. The industry poses strict demands for inspection and maintenance. High focus on asset integrity and cost-efficient operations. Information retrieval and preventive maintenance reduce costly repairs. Often unnecessarily costly to use conventional ROVs for inspection and light intervention. GROWING DEMAND FOR LIGHTER, LESS COSTLY, AND MORE SPECIALIZED VEHICLES
EXISTING TECHNOLOGY Inspection ROV AUVs I-AUVs Photo: Remus 100 AUV by Kongsberg Maritime Photo: Munin AUV by Kongsberg Maritime Photo: SAUVIM by Autonomous Systems Laboratory, University of Hawaii Photo: Seaeye Falcon by Saab Seaeye Photo: AIV by Subsea 7 Photo: Seaeye Sabertooth by Saab Seaeye Photo: Girona 500 by Vicorob
The Underwater Swimming Manipulator A Bio-Inspired AUV
THE UNDERWATER SWIMMING MANIPULATOR A BIO-INSPIRED AUV Length: 1.8 m Mass: 8 kg Length: 3.4 m Mass: 85 kg
MAIN ADVANTAGES
APPLICATIONS Subsea inspection and light intervention Planned and on demand Support during underwater installation and construction Provide additional camera view during ROV operations Pipeline surveys Harbor security and ship hull inspections Support for marine archeology Support for marine biology
Modelling the USM Multi-body kinematics and dynamics State dependent thruster configuration
MULTI-BODY KINEMATICS Modelled as a floating-base underwater manipulator with one or two arms Using homogeneous transformations to describe the kinematic relations Robot velocity state 1 Sverdrup-Thygeson et. al., Journal of Oceanic Engineering (accepted)
MULTI-BODY KINEMATICS Using adjoint maps to describe relations between the body-fixed velocities Velocity of each link relative to inertial frame geometric link Jacobian 1 Sverdrup-Thygeson et. al., Journal of Oceanic Engineering (accepted)
MULTI-BODY DYNAMICS Floating base manipulator in an underwater environment Depends on the joint angles q time-varying matrices Calculated using the geometric link Jacobian, e.g., single body inertia inertial coupling
Control of the USM Kinematic redundancy Strong dynamic coupling Unknown properties and hydrodynamic parameters Location of CM and CB depends on the joint angles Constrained thrust allocation Docking
MOTION CONTROL FRAMEWORK Kinematic control Resolves the kinematic redundancy, generates desired velocities Dynamic control Computes required forces and moments Thrust allocation Distributes the thrust forces 1 Sverdrup-Thygeson et. al., Journal of Oceanic Engineering (accepted)
MOTION CONTROL FRAMEWORK Very strong coupling between the commanded joint motion and the overall motion Inertial forces Drag forces Restoring forces and moments The joint motion changes the thruster configuration and thus, it affects the ability to satisfy the commanded forces and moments
KINEMATIC CONTROL Multiple task priority inverse kinematic control Objectives Control the position/orientation of one or both ends of the robot Satisfy the mechanical constraints Avoid singular thruster configurations Avoid singular joint configurations 1 Avoid collisions Minimize the induced motion of the base Minimize the energy consumption 1 Sverdrup-Thygeson et. al., CCTA 2017, Mauna Lani, HI, USA
DYNAMIC COUPLING Figure: Fixed base vs floating base. Created by Morten F. Amundsen.
DYNAMIC COUPLING OPTION 1 Compensate using the thrusters a) Estimate the hydrodynamic forces caused by the joint motion Requires good model knowledge May require a lot of thruster effort b) Use robust control techniques to suppress the joint motion disturbance Sliding mode control Higher-order sliding mode controller 1 1 Borlaug et. al., SWARM 2017, Kyoto, Japan
DYNAMIC COUPLING OPTION 2 Compensate using the joints a) Predict the resulting motion of the base 1 Using the Generalized Jacobian from space robotics Based on law of conservation of momentum Not valid under water May still be of practical use for slow joint motion b) Measure the actual velocity of the base 2 Compensate using kinematic control c) Control the orientation of the base using the joints Also from space robotics 1 Amundsen et.al., submitted to ECC 2017 2 Jørgensen and Schjølberg, ECC 2016, Aalborg, Denmark Figure: End-effector positioning using Generalized Jacobian. Created by Morten F. Amundsen.
THRUST ALLOCATION Compute the state dependent thruster configuration matrix Solve the constrained thrust allocation problem depends on the joint angles Minimize thruster utilization or total power consumption Constrained by the physical limitations of the thrusters, max/min limits and rate of change Explicit solution using redistributed pseudo-inverse thrust allocation Optimal solution using linear or quadratic optimization methods
DOCKING Video created by Albert Sans Muntadas
WHAT S NEXT? Compare and confirm the applicability of the presented methods, both in simulation and experimentally
THANK YOU FOR YOUR ATTENTION APPLICATIONS AND CHALLENGES FOR UNDERWATER SWIMMING MANIPULATORS Jørgen Sverdrup-Thygeson AMOS Days October 2017