M. O. Tokhi

Command shaping techniques for vibration control of a flexible robot manipulator

Abstract This paper presents an investigation into development of feed-forward control strategies for vibration control of a flexible robot manipulator using command shaping techniques based on input shaping, low-pass and band-stop filtering. A constrained planar single-link flexible manipulator is considered and the dynamic model of the system is derived using the finite element method. An unshaped bang–bang torque input is used to determine the characteristic parameters of the system for design and evaluation of the control techniques. Feed-forward controllers are designed based on the natural frequencies and damping ratios of the system. Simulation results of the response of the manipulator to the shaped and filtered inputs are presented in time and frequency domains. Performances of the techniques are assessed in terms of level of vibration reduction at resonance modes, speed of response, robustness and computational complexity. The effects of number of impulse sequence and filter order on the performance of the system are investigated. Finally, a comparative assessment of the input shaping and input-filtering techniques is presented and discussed.

Active sound and vibration control: theory and applications

This book presents the established fundamentals in the area of active sound and vibration control as well as exploring the new and emerging technologies and techniques. There has been a considerable amount of effort devoted to the development and realisation of methodologies for control of sound and vibration, and this book covers the latest theoretical, algorithmic and practical applications including: noise control in 3D propagation, adaptive algorithms, prediction, processing and tuning, neuro-active control, control of microvibrations, and noise reduction in locomotives and vehicles.

Vibration control of a single-link flexible manipulator using command shaping techniques

Abstract This paper presents experimental investigations into the development of feed-forward control strategies for vibration control of a flexible manipulator using command shaping techniques based on input shaping and low-pass and band-stop filtering. A laboratory-scale single-link flexible manipulator is used and various system responses are obtained. Initially, an unshaped bang-bang torque input is used to determine the dynamic response parameters of the system for design and evaluation of the control techniques. Feed-forward controllers are then designed based on the natural frequencies and damping ratios of the system. Experimental results of the response of the manipulator to the shaped and filtered inputs are presented in time and frequency domains. Performances of the techniques are assessed in terms of level of vibration reduction at the natural frequencies, time response specifications, robustness to natural frequency variation and processing time. The effects of the number of impulses and filter order on the performance of the system are investigated. Finally, a comparative assessment of input shaping and filtering techniques is presented.

Dynamic characterisation of a flexible manipulator system

This paper presents theoretical and experimental investigations into the dynamic modelling and characterisation of a flexible manipulator system. A constrained planar single-link flexible manipulator is considered. A dynamic model of the system is developed based on finite element methods. The flexural and rigid dynamics of the system as well as inertia effects and structural damping are accounted in the model. Performance of the algorithm in describing the dynamic behaviour of the system is assessed in comparison to an experimental test-rig. Experimental results are presented for validation of the developed finite element model in the time and frequency domains.

Soft computing-based active vibration control of a flexible structure

Control of vibration of flexible structures has been of remarkable research attention in the last decade. Conventional control methods have not been widely successful due to the dynamic complexity of flexible structures. The literature has recently seen an emergence of demand of soft computing techniques in modelling and control of such dynamic systems. However, the form of soft computing required depends on the nature of the application. This paper accordingly presents investigations into modelling and control techniques based on soft computing methods for vibration suppression of two-dimensional flexible plate structures. The design and analysis of an active vibration control (AVC) system utilising soft computing techniques including neural networks and fuzzy logic is presented. The investigation involves soft computing approach with single-input single-output (SISO) and single-input multi-output (SIMO) AVC structures. A comprehensive comparative assessment of the approaches in terms of performance and design efficiency is also provided. Investigations reveal that the developed soft computing-based AVC system performs very well in the suppression of vibration of a flexible plate structure. It is also shown that the developed SIMO AVC system performs much better in the suppression of vibration of a flexible plate structure in comparison to the SISO AVC system.

Hybrid fuzzy logic control with genetic optimisation for a single-link flexible manipulator

To reduce the end-point vibration of a single-link flexible manipulator without sacrificing its speed of response is a very challenging problem since the faster the motion, the larger the level of vibration. A conventional controller can hardly meet these two conflicting objectives simultaneously. This paper presents a genetic algorithm (GA)-based hybrid fuzzy logic control strategy to achieve that goal. A proportional-derivative (PD) type fuzzy logic controller utilising hub-angle error and hub-velocity feedback is designed for input tracking of the system. GA is used to extract and optimise the rule base of the fuzzy logic controller. The GA fitness function is formed by taking the weighted sum of multiple objectives to trade off between system overshoot and rise time. Moreover, scaling factors of the fuzzy controller are tuned with GA to improve its performance. A GA-based multi-modal command shaper is then designed and augmented with the fuzzy logic controller to reduce the end-point vibration of the system. The performance of the hybrid control scheme is assessed in terms of its input-tracking capability and vibration suppression at the end point. A significant amount of vibration reduction has been achieved at the end point, especially at the first three resonance modes of the rig structure, with satisfactory level of overshoot, rise time, settling time, and steady-state error.

Designing feedforward command shapers with multi-objective genetic optimisation for vibration control of a single-link flexible manipulator

This paper presents investigations into the design of a command-shaping technique using multi-objective genetic optimisation process for vibration control of a single-link flexible manipulator. Conventional design of a command shaper requires a priori knowledge of natural frequencies and associated damping ratios of the system, which may not be available for complex flexible systems. Moreover, command shaping in principle causes delay in systems response while it reduces system vibration and in this manner the amount of vibration reduction and the rise time conflict one another. Furthermore, system performance objectives, such as, reduced overshoot, rise time, settling time, and end-point vibration are found in conflict with one another due to the construction and mode of operation of a flexible manipulator. Conventional methods can hardly provide a solution, for a designer-oriented formulation, satisfying several objectives and associated goals as demanded by a practical application due to the competing nature of those objectives. In such cases, multi-objective optimisation can provide a wide range of solutions, which trade-off these conflicting objectives so as to satisfy associated goals. A multi-modal command shaper consists of impulses of different amplitudes at different time locations, which are convolved with one another and then with the desired reference and then used as reference (for closed loop) or applied to system (for open loop) with the view to reduce vibration of the system, mainly at dominant modes. Multi-objective optimisation technique is used to determine a set of solutions for the amplitudes and corresponding time locations of impulses of a multi-modal command shaper. The effectiveness of the proposed technique is assessed both in the time domain and the frequency domain. Moreover, a comparative assessment of the performance of the technique with the system response with unshaped bang-bang input is presented.

Nonlinear modelling of a twin rotor MIMO system using radial basis function networks

Modelling of innovative aircraft such as UAVs, X-wing, tilt body and delta-wing is not easy. This paper presents a nonlinear system identification method for modelling air vehicles of complex configuration. This approach is demonstrated through a laboratory helicopter. Extensive time and frequency-domain model-validation tests are employed to instil confidence in the estimated model. The estimated model has a good predictive capability and can be utilized for nonlinear flight simulation studies. The approach presented is suitable for modelling new generation air vehicles.

Dynamic modelling of a single-link flexible manipulator: parametric and non-parametric approaches

This paper presents an investigation into the development of parametric and non-parametric approaches for dynamic modelling of a flexible manipulator system. The least mean squares, recursive least squares and genetic algorithms are used to obtain linear parametric models of the system. Moreover, non-parametric models of the system are developed using a non-linear AutoRegressive process with eXogeneous input model structure with multi-layered perceptron and radial basis function neural networks. The system is in each case modelled from the input torque to hub-angle, hub-velocity and end-point acceleration outputs. The models are validated using several validation tests. Finally, a comparative assessment of the approaches used is presented and discussed in terms of accuracy, efficiency and estimation of the vibration modes of the system.

Parametric modelling of a twin rotor system using genetic algorithms

System identification using parametric linear approaches for modelling a twin rotor multi-input multi-output system (TRMS) in hovering position is presented in this work. The utilisation of a genetic algorithm (GA) optimisation technique for dynamic modelling of a highly non-linear system is studied in comparison to the conventional recursive least squares (RLS) technique. The global search technique of GA is used to identify the parameters of the TRMS based on one-step-ahead prediction. A comparative assessment of the two models in characterising the system is carried out in the time and frequency domains. Experimental results indicate the advantages of GA over RLS in linear parametric modelling. The developed genetic-modelling approach will be used for control design and development in future work.