Finn Conrad

A singular value sensitivity approach to robust eigenstructure assignment

A design technique for improving the feedback properties of multivariable state feedback systems designed using eigenstructure assignment is presented. Based on a singular value analysis of the feedback properties a design parameter adjustment procedure is outlined. This procedure allows for the preservation of important properties of the initial design, by selecting only a subset of the design parameters for adjustment. The computational requirements are modest and straight-forward to implement with standard software. An example illustrating the method is included.

Hybrid Control of a Robot - A Case Study

An experiment with a distributed architecture to support a hybrid controller for a robot is described. For a desired trajectory, the controller plans a schedule for switching between a fixed set of control functions. Initial results indicate that the proposed architecture is better at achieving a desired trajectory than conventional control algorithms. The experiment also illustrates a division of concerns between software engineering and control engineering. Development of controlling realtime state machines and their mapping to processors and network is the task of software engineering, while the control engineer must identify plant phases, switching conditions and relevant control laws. These define algorithms for a planner and for the control functions. The format of schedules produced by the planner and the algorithms constitute the interface to software developers.

Identification for Modeling And Adaptive Control of Hydraulic Robot Manipulators

Abstract This paper describes the practical application of system identification methods to obtain a transfer function representation of the open-loop dynamics of an electrohydraulic actuator. The data are processed by instrumental variable algorithm. The obtained model is intended to provide a basis for control system design and simulation study. The identified model has been evaluated, respectively, by applying spectral analysis and simulation. Results show that accurate models were obtained.

Eigenstructure and residuals in multivariable state-feedback design

Abstract In this paper it is shown that all residuals assignable by state feedback must belong to certain well-defined subspaces defined by the freely selectable closed-loop eigenvalues. These subspaces are straightforward to compute, and the computational requirements are modest. The applicability of this result is facilitated by the fact that fundamental control design objectives like I/O response and robustness can be expressed in terms of residuals. A design procedure is outlined and illustrated by an example. The method is applicable to square and non-square systems.

Design of Over Center Valves Based on Predictable Performance

A typical over center valve system and a time domain simulation model is introduced together with a hypothesis that flow force compensation should reduce the inherent oscillatory behavior of such systems. A few results are shown from a parameter study that confirms this assumption and an approach to design over center valve geometries that have negative flow forces is presented with emphasis on predictability. In conclusion it is made clear that negative flow forces in the over center valve cannot solve the instability problem in general, however, it might very well be a method like lowering the pilot ratio, that can be used to application specific instability problems.Copyright

IT-Tools Concept for Simulation and Design of Water Hydraulic Mechatronic Test Facilities for Motion Control and Operation in Environmentally Sensitive Application Areas

This paper presents a proposed IT-Tools concept for modeling, simulation, analysis and design of water hydraulic actuators for motion control of machines, lifts, cranes and robots. The designed test rigs have tap water hydraulic components of the Danfoss Nessie® product family and equipped with a measurement and data acquisition system. Results of the mathematical modeling, simulation and design of the motion control test rigs are presented. Furthermore, the paper presents selected experimental and identifying test results for the water hydraulic test rigs.© 2004 ASME

Linear Perturbation Adaptive Control of Hydraulically Driven Manipulators

A method for synthesis of a robust adaptive scheme for a hydraulically driven manipulator, that takes full advantage of any known system dynamics to simplify the adaptive control problem for the unknown portion of the dynamics is presented. The control method is based on adaptive perturbation control. Using the Lyapunov approach, under slowly time-varying assumptions, it is shown that the tracking error and the parameter error remain bounded. This bound is a function of the ideal parameters and a bounded disturbance. The control algorithm decouples and linearizes the manipulator so that each joint behaves as an independent second-order system with fixed dynamics.Copyright

Robust Control of Oscillations in Agricultural Tractors

This paper relates to analyses and control of the oscillations occurring in many off road vehicles, which are designed without any suspension. Without suspension, the tire is the only elastic element acting between the vehicle and the ground but the suspension and damping properties of the tires cannot meet the demands for fast, safe and comfortable road transportation. In this paper the above-mentioned phenomenon is investigated with special focus on agricultural tractors. A control strategy is developed to make the implement counteract the movement of the tractor and thereby reducing the pitching oscillation. The control strategy is based on a linear plant model with constant or slowly varying parameters. Using a frequency-response approach the disturbance rejection is made effective over a significant portion of the system bandwidth. To improve robustness with respect to bounded disturbances (from the road) natural frequencies for the vehicle and implement is identified and the controller parameters tuned adaptively based on an optimization formulation.Copyright

Experimental Modelling of Variable Displacement Radial Piston Pumps by Using a Bi-Directional Computer-Controlled Hydraulic Dynamometer

Abstract An experimental modelling method for hydraulic pumps based on experimentally obtained data using statistical teclmiques is proposed and a needed bi-directional computer controlled hydraulic dynamometer system is briefly described. Comparing to the existing theoretical models, this method can provide an empirical model with higher accuracy and validation so that the requirement of system design, simulation and fault diagnose can be satisfied. A modelling result of a variable displacement radial piston pump as an example is presented and discussed in this paper.

ROPSIM, A ROBOT OFF-LINE PROGRAMMING AND REAL-TIME SIMULATION SYSTEM INCLUDING DYNAMICS

Abstract A new architecture for a model driven robot programming and real-time simulation system, ROPSIM, is presented and discussed. The new features of the system is described, such as neutral interface communication at input/output level using the ISO standard proposals STEP (extended) and ICR. Further the ROPSIM is based on the use of generic models for sensors, robot controller and robot arm geometry and kinetics in order to avoid dependency of dedicated robot models. The software is developed using the language C++ and key modules of the system is shortly described.