Petko Kiriazov

Robust feedback stabilization of underwater robotic vehicles

The controlled motion of an underwater vehicle is very likely to be affected by arbitrary disturbances with considerable magnitudes. In this paper, we develop a simple approach for optimal robust control design of underwater robotic vehicles having decentralized input-output structure. Our design method is based on an explicit condition on the control input matrix which has been found to be necessary and sufficient for a decentralized control system to be robust against arbitrary, but otherwise, bounded disturbances. That makes it possible to get optimal trade-off relations between the bounds of disturbances, the system output accuracy, and the control force limits. For the robust control design purpose, we apply decentralized sliding-mode control the stability of which can be easily verified using Lyapunov theory. In order to show the effectiveness of the design method, the controlled planar motion of an underwater robotic vehicle is taken as an illustrative example.

Efficient Approach for Dynamic Parameter Identification and Control Design of Structronic Systems

The proposed study addresses various-type structronic systems (SS) like robots having elastic joints/links or engineering structures with vibration/shape control. SS can be considered as functionally directed compositions of mutually influencing subsystems: control, actuator, structural, and sensor subsystems. Actuators may be of various-type, e.g., electrical motors, electro-hydraulic cylinders, piezo-electric, electro-magnetic actuators. SS may have, therefore, highly complex dynamics and the parameters describing them are often very difficult or impossible to estimate with the required accuracy. To model and control such complex mechanical systems is a challenging problem and one that has been addressed by many researchers, [5, 6, 7], [10], [15].

POINT-TO-POINT MOTION OF ROBOTIC MANIPULATORS: DYNAMICS, CONTROL SYNTHESIS AND OPTIMIZATION

Abstract A new input—output approach is proposed for the solution of a problem for optima1 control synthesis of robotic manipulators in point—to point operation. The performance index is a weighted minimum time-energy loss criterion in the presence of control and state constraints. A direct search optimization procedure is suggested miaking use of first-order spline approximations of optimal control laws. The given Two-Point Boundary Value Problem (TPBVP) is reduced Lo the solution of a vector shooting equation with respect Lo the final switching Limes of the test control functions. The optimization procedure is performed over the set of all other parameters describing the spline control functions. A simple weak condition on the inertia matrix is shown Lo be sufficient for the existence of feasible solutions. A dynamic model of a Lwo-degree of freedom manipulator is Laken Lo illustate the efficiency of this control synthesis procedure.

On control design in simulation of human motion

Abstract Efficient simulation of articulated structures is needed in biomechanical engineering, human animation, virtual reality, and robotics. A conceptual framework for control design in constrained and unconstrained motion tasks is developed. In the first case, decentralized sliding-mode controllers with maximum degree of robustness can be designed. In the other case, simple but consistent with Pontryagins Maximum principle test functions are employed whose parameters are determined through a fast converging shooting procedure. Besides the analytical guarantees, we verify the efficiency of our approach in dynamic simulation of standing-tip motion where both open-loop and closed-loop controllers are implemented.

On Direct-Search Optimization of Biped Walking

Employing a set of appropriate test control functions, the optimal control synthesis task is transformed into a series of control parameter optimization problems. The direct-search optimization procedure was verified on the dynamic model of a five-link anthropomorphic walking mechanism. The structure and the shapes of the synthesized control and state functions are similar to those of the humans. The numerical results show very efficient energy-loss minimization which means that the so-called synergism with the human bipeds, can be obtained with the controlled walking machines, too.

Intelligent control design in robotics and rehabilitation

For control purposes in robotics or rehabilitation, we may use properly simplified dynamic models with a reduced number of degrees of freedom. First, we define a set of variables that best characterize its dynamic performance in the required motion task. Second, driving forces/torques are properly assigned in order to achieve the required dynamic performance in an efficient way. The usual performance requirements are for positioning accuracy, movement execution time, and energy expenditure. We consider complex biomechatronic systems (BMS) like human with active orthosis or robotic arm that have to perform two main types of motion tasks: goal-directed movements and motion/posture stabilization. We propose new design concepts and criteria for BMS based on necessary and sufficient conditions for their robust controllability. Using simplified, yet realistic, models, we give several important examples in robotics and rehabilitation to illustrate the main features and advantages of our approach.

Robust Controllability of Underwater Vehicles and Their Design Optimization

Abstract There are various designs and control tasks for marine systems (MS), where continuously increasing demands for higher speed, improved motion accuracy, and reduced energy consumption are to be satisfied. In order to achieve such complicated performance optimization, it is very important to study MS controllability and their design criteria. An explicit, necessary and sufficient condition has been found to guarantee robustness of decentralized controllers against arbitrary, but bounded disturbances. Thus the feedback control design can be based on optimal trade-off relationships between the bounds of disturbances and the control force limits. These and other reasonable design criteria will be considered in this paper. The design concepts will be illustrated with several examples concerning shape, mass distribution, as well as actuators sizes and locations of controlled MS.

Integrated Structure-control Design of Dynamically Walking Robots

This study is motivated by the need of dynamics-based methodologies for overall design of legged robots (LR). Along with the basic design requirement for strength/load capacity, additional design criteria for LR are needed to meet the continuously increasing demands for faster motion, higher position accuracy and reduced energy consumption. A conceptual framework for their integrated structure-control design is proposed that can be used to create LR with maximum capability to achieve the required dynamic performance. To verify our design optimisation concepts, several interesting examples regarding two- and four-LR are considered.

Optimal Robust Controllers for Multibody Systems

The proposed paper addresses control design problems for multibody systems (MBS) like robot manipulators or mechanical structures with active vibration damping. When performing motion tasks, such systems may be subject to even severe disturbances. A control design approach for motion stabilisation has to meet the increasing demands for faster response, higher position accuracy, and reduced energy consumption. A central role in solving such a complicated control optimisation problem plays the matrix that transfers the control inputs into mechanical accelerations. For MBS having as many control forces as controlled outputs, simple conditions on that matrix are found to be necessary and sufficient for such systems to be controllable in the presence of bounded random disturbances. There are proposed optimal trade-off relations for designing decentralised controllers with maximum degree of robustness. An interesting extension of these concepts to the important class of over-controlled MBS is proposed. Examples with a car body suspension and an elastic-joint manipulator are presented to show how the proposed control design approach can be applied and developed.

On Optimal Control of Marine Systems

Abstract A unified optimization approach is proposed which leads to efficient feedforward and feedback control of various-type marine systems (MS). For the feedforward control synthesis, a direct-search optimization algorithm is developed, in which parameterized control laws consistent with Pontryagin’s maximum principle are used. The given two-point boundary-value problem is transformed into a system of shooting equations with guaranteed existence of solutions. The feedback control design is based on optimal trade-off relationships between bounds of disturbances and control force limits. The control optimization approach is applied to a full dynamic model of an underwater vehicle in the case of planar motion.