Proceedings of the Institution of Mechanical Engineers,Part I: Journal of Systems and Control Engineering

This paper presents a review of a number of state-of-the-art non-linear control design techniques which may be readily applied to solve practical problems in a robust fashion. It is first shown that non-linear controllers may be designed using straightforward linear models with minimal recourse to abstract mathematical concepts. More involved philosophies for robust control system design of inherently non-linear plants are then briefly described. A straightforward yet rigorous design framework is then presented to implement the philosophy. Tutorial examples are presented throughout the paper in order to illustrate major points of interest.

Decoupling control of robotic manipulators, based on a dynamic model that includes both the mechanical dynamics of the links and the electrical dynamics of the joint motors, is studied in this paper. By using an algorithm of feedback linearization developed in this paper, the highly non-linear and strongly cross-coupled electromechanical system is decoupled and linearizd into a set of decoupled linear subsystems. Then, disturbance decoupling is further conducted for disturbance and uncertainty attenuation. It is shown that, by using the proposed control scheme, both modelling difficulty and control complexity of the manipulator system can be significantly reduced.

In robotics, despite considerable effort to minimize system modelling errors, uncertainties are always present and sometimes significant. In this paper, modelling errors are first represented by a class of bounded disturbances in the input channels (torques) of the robot. A measure of the robot system's ability to reject these disturbances is formulated in an L₂ gain sense and a control design is subsequently proposed to achieve optimal disturbance rejection. If more detailed information is available on the plant-model mismatch, then the control design can be modified to incorporate an adaptive scheme (with explicit parameter updating laws) in order to reduce the conservativeness of the original design and to improve robust performance of the overall system.

In this paper, a parallel adaptive neural network (NN) control design for robots motivated by the work by Lee and Tan is presented. The controller is based on direct adaptive techniques and an approach of using an additional parallel NN to provide adaptive enhancements to a basic fixed controller, which can be either a NN-based non-linear controller or a model-based non-linear controller. It is shown that, if Gaussian radial basis function networks are used for the additional parallel NN, uniformly stable adaptation is assured and asymptotic tracking of the position reference signal is achieved.

The development of a fuzzy control system for a closed-die hot-forging machine is described. Details of the input and output fuzzy variables and the fuzzy inference procedure are given. Results obtained using the fuzzy control system are presented. These demonstrate the ability of the system accurately to control the amount of energy delivered to the workpiece to keep it within narrow tolerances without overloading the die.

An approach is presented whereby a number of faults, typical of many hydraulic circuits, may be determined using rule-based concepts. The approach uses on-line data and principally integrates both qualitative and quantitative reasoning in a novel way that enables speciJic faults to be detected. It has the advantage of being able to indicate a class of multiple faults and can also provide some indication of sensor integrity. A practical example is presented using an open-loop meter-inlmeter-out flow control system, and a variety of single and multiple faults have been studied with respect to leakages, check valves andflow control valve behaviour.

This paper presents the design and performance evaluation of an adaptive active control mechanism for vibration suppression inflexible beam structures. A cantilever beam system in transverse vibration is considered. First-order central finite difference methods are used to study the behaviour of the beam and develop a suitable test and verification platform. An active vibration control algorithm is developed within an adaptive control framework for broadband cancellation of vibration along the beam using a single-input multi-output (SIMO) control structure. The algorithm is implemented on a digital processor incorporating a digital signal processing (DSP) and transputer system. Simulation results verifying the performance of the algorithm in the suppression of vibration along the beam, using single-input single-output and SIMO control structures, are presented and discussed.