Adaptive robot control with a second order sliding component

Two adaptive robot controllers, both with a second order sliding mode component, are proposed and compared. The two controllers have the same basic structure, have provable tracking error convergence, but their suitability for implementation in practice is markedly different. It appeared that one of the proposed control laws has favorable characteristics, both on theoretical as well as on practical grounds, and did perform quite well in a realistic simulation and in an experiment with a mechanical system with significant unmodeled dynamics. Compared with previous experimental results obtained with a variety of other control laws, the new controller did quite wel

The use of symbolic computation in nonlinear control: is it viable?

To aid in the analysis and design of nonlinear control systems the NONlinCON package (an acronym for Nonlinear Control) has been developed. This paper addresses the usefulness of the NONlinCON package as a self contained tool in the symbolic analysis and design of nonlinear control systems, as a replacement and/or complement for numerical tools, and as a substitute for analytical (paper and pencil) work. The symbolic computation program MAPLE is used as a computing substrate for NONlinCON. To assess the viability of this tool several algorithms available for analysis and design are implemented in the package, and applied to examples of textbook problems with published solutions and also to a larger scale problem. It is concluded that, at the present state, symbolic computation is a viable approach for straightforward textbook problems, but not grown up enough to tackle larger problem

Generalized normal forms and disturbance rejection : a symbolic approach

The paper employs a symbolic approach, making use of the computer algebra system MAPLE and the NONCON package, to compute (1) a generalized normal form for systems without a well-defined relative degree using the zero dynamics algorithm and (2) a state feedback that achieves disturbance rejection or decoupling with an implementation of an algorithm for the maximal controlled invariant distribution. A few examples illustrate the power of the approach, but only for rather simple problems. Due to the complexity of the (implementation of the) algorithms it seems unlikely that large scale problems are efficiently solvable symbolicall

Linear and nonlinear H\sb \infty control : an example

The development of linear and nonlinear H/sub infinity / controllers for a monocycle is outlined. Specifications for the design emphasize performance with limited control activity. The controllers are shown to have slightly different stabilization properties, but the L/sub 2/-gain of the system with the nonlinear H/sub infinity / controllers is slightly better and they may realize a faster tracking response by using larger control action

Second order sliding mode control with adaptation

The paper proposes a new control scheme for nonlinear robotic systems. The basis of the scheme is an existing second order sliding mode controller augmented with an adaptive component. A computed torque-like adaptive controller with a second order system type of measure of tracking accuracy is the source of the adaptation law. Extensive simulations of a nonlinear robotic system with one rotational and one translational degree-of-freedom unmodeled actuator dynamics and parameter mismatch, confirm the suitability of the proposed scheme. The adaptation law allows smaller feedback gains to be used, and thus improves the robustness without degrading the performance. Adaptation may also improve the performance when unmodeled actuator dynamics is present, although to a lesser degree and not uniformly. The stability robustness in this case is slightly wors

Adaptive second order sliding-mode control for rigid robots

A novel robot controller is proposed, borrowing ideas from sliding mode and adaptive control. It is a mix between a computed torque and a passivity based controller and uses a second order measure of tracking accuracy. The paper provides ample evidence, by convergence analysis, simulations, and experiments, that the new controller will function well in practice. Based on the results, the controller seems to be a welcome addition to the class of tracking controllers for rigid robots with significant parameter uncertaint

Robust control of mechanical systems: a computational design study

Methods for the design of robust controllers for nonlinear systems, especially manipulators, are investigated with emphasis on robustness for unmodeled dynamics. The system to be controlled is a two-degree-of-freedom manipulator, with a rotational and a prismatic joint. The control task is to follow a circular object with trajectory control along the circumference and force control in the direction perpendicular to the circumference. For the trajectory a fixed computed torque with a PD (proportional plus derivative) controller is used. The force is controlled by the controllers under investigation. These controllers are all based on a linearizing state-feedback with acceleration feedforward, and a controller based on a H/sub 2/ or H/sub infinity / design for the resulting linear system. A PD controller is used for referenc

Mass optimized self-actuated panels for several truss core topologies

Sandwich panels with truss cores offer possibilities for self-actuation.They are analyzed, with emphasis on mass optimal design for failureand stiffness.It is shown that introducing additional freedom in selectingthe topology of tetrahedral or pyramidal cores, by1) making the core units, or even all core members, disjoint, so varying the distance between core units becomes possible,2) using multiple layers,brings significant advantages.For some conditions, the performance of the modified panel becomesbetter by a factor of two, causing actuated truss core panels to performat least as well as, or even better than, panels with, \eg honeycomb cores,that do not easily allow core actuation.A special case of the analysis is the mass optimaldesign of panels with 3D-Kagom\'e truss units, which canbe regarded as a special geometry for a tensegrity prism