Rogelio Lozano-Leal

Model reference robust adaptive control without a priori knowledge of the high frequency gain

A novel model-reference robust adaptive controller that does not require a priori knowledge of the high-frequency-gain sign is proposed. The scheme is applicable to minimum-phase plants of arbitrary relative degree and ensures that in the absence of unmodeled dynamics the tracking error converges to zero and all the signals remain bounded. The control law uses a particular projected parameter vector instead of the current estimates to avoid division by zero. >

Point-to-point regulation of a robot with flexible joints including electrical effects of actuator dynamics

This paper considers the set-point tracking problem in rigid and flexible-joint robots when both the mechanical as well as the electrical effects of the actuator dynamics are taken into account. The suggested controllers are based on state and output feedbacks. The current approach demonstrates that for every given desired operating point, linear state and output feedbacks with constant feedforwards can be constructed such that the closed-loop system is globally asymptotically stable.

Strictly positive real transfer functions revisited

The two most commonly used definitions of strictly positive real (SPR) transfer functions are reviewed. Contrary to what has been previously suggested, it is shown that the least restrictive (weak) definition of the two is clearly related to the Yacubovich-Kalman lemma. A relationship between time and frequency domain conditions pertaining to the weak definition of SPR systems is established. An alternative proof is given to show that a PR plant is stabilized by any (weak) SPR system connected in negative feedback.<<ETX>>

Adaptive control of a class of first order nonlinear systems without a priori information on the plant parameters

An adaptive control for a class of first-order nonlinear systems is presented. The control scheme is free from singularities (i.e. division by zero). This has been achieved by appropriately modifying the plant parameter estimates before using them in the control input generation. The proposed control algorithm achieves global asymptotic model tracking and the control laws denominator is uniformly bounded away from zero without assuming any prior knowledge of the plant parameters.<<ETX>>

Adaptive algorithm for force/position control of flexible joint manipulators with holonomic constraints

The authors present an adaptive force/position control strategy for flexible joint robot manipulators subject to holonomic constraints. Convergence and stability results are guaranteed regardless of the joint flexibility value, in the non-adaptive as well as in the adaptive case. The joint flexibility matrix can be incorporated into the parameter vector of the adaptive controller. When the system physical parameters are unknown, an additional assumption is needed, i.e., the constraints are assumed to be linear.<<ETX>>

Singularity-free adaptive pole-placement without resorting to persistency of excitation-detailed analysis for first order systems

The development of adaptive control algorithms for possible nonminimum phase systems has been hampered by singularities that may arise in the control law. A way is presented to circumvent singularities in adaptive pole placement control algorithms. The analysis is detailed for a first-order system. The modifications to the estimates are explicitly given.<<ETX>>

Adaptive pole placement of non-minimum phase systems with bounded disturbances

This paper presents globally convergent indirect adaptive control scheme for plants which are not necessarily minimum phase and are subject to bounded disturbances.