18 research outputs found
On a switching control scheme for nonlinear systems with ill-defined relative degree
This paper discusses the applicability of a switching control scheme for a nonlinear system with ill-defined relative degree. The control scheme switches between exact and approximate input-output linearisation control laws. Unlike a linear system under a switching control scheme, the equilibria of a nonlinear system may change with the switching. It is pointed out that this is not sufficient to cause instability. When the region of the approximate linearisation control law is attractive to the exact zero dynamics, it is possible that the closed-loop system under the switching control scheme is still stable. The results in this paper shows that the switching control scheme proposed in Tomlin and Sastry (Systems Control Lett. 35(3) (1998) 145) is applicable for a wider class of nonlinear systems
Model predictive control of nonlinear systems: computational burden and stability
Implementation of Model Predictive Control (MPC) for nonlinear systems requires
on-line solution of a non-convex, constrained nonlinear optimisation problem.
Computational delay and loss of optimality arise in the optimisation procedures.
This paper presents a practical MPC scheme for nonlinear systems with
guaranteed asymptotic stability. It is shown that when an initial control profile is
chosen to satisfy an inequality condition in each on-line optimisation procedure,
the nonlinear system under the proposed nonlinear MPC is asymptotically stable.
The stability condition presented in this paper enables the “fictitious” terminal
control to be nonlinear, rather than only linear, and thus the stability region is
greatly enlarged. Furthermore it is pointed out that nominal stability is still guaranteed
even though the global, or even the local, minimisation of the objective
cost is not achieved within the prescribed computational tim
A nonlinear disturbance observer for robotic manipulators
A new nonlinear disturbance observer (NDO)
for robotic manipulators is derived in this paper. The global
exponential stability of the proposed disturbance observer (DO)
is guaranteed by selecting design parameters, which depend
on the maximum velocity and physical parameters of robotic
manipulators. This new observer overcomes the disadvantages of
existing DO’s, which are designed or analyzed by linear system
techniques. It can be applied in robotic manipulators for various
purposes such as friction compensation, independent joint control,
sensorless torque control, and fault diagnosis. The performance of
the proposed observer is demonstrated by the friction estimation
and compensation for a two-link robotic manipulator. Both
simulation and experimental results show the NDO works well
Non-linear PID predictive controller
A new class of nonlinear PID controllers are derived for nonlinear systems using a Nonlinear
Generalised Predictive Control (NGPC) approach. First the disturbance decoupling ability of
the nonlinear generalised predictive controller is discussed. For a nonlinear system where the
disturbance cannot be decoupled, a nonlinear observer is designed to estimate the offset. By
selecting the nonlinear gain function in the observer, it is shown that the closed-loop system
under optimal generalised predictive control with the nonlinear observer is asymptotically stable.
It is pointed out that this composite controller is equivalent to a nonlinear controller with integral
action. As a special case, for a nonlinear system with a low relative degree, the proposed
nonlinear controller reduces to a nonlinear PI or PID predictive controller, which consists of a
nonlinear PI or PID controller and a prediction controller. The design method is illustrated by
an example nonlinear mechanical system
Transient motion of a circular plate after an impact
The transient response of a flat circular plate to a sudden impact has been studied experimentally and theoretically. High-speed electronic speckle pattern interferometry reveals the presence of pulses that travel around the edge of the plate ahead of the bending motion initiated by the strike. It is found that the transient motion of the plate is well described by Kirchhoff thin-plate theory over a time approximately equal to the time required for the initial impulse to circumvent the plate; however, a more sophisticated model is required to describe the motion after this time has elapsed
The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy
Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations.
Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves.
Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p 90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score.
Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care