Steve Hand

Non-fragile H ∞ control for half-vehicle active suspension systems with actuator uncertainties

In this paper we investigate the problem of non-fragile H∞ controller design for active suspension systems with actuator uncertainty constraints. A half-vehicle model with active suspension system is considered in this paper, the vehicle dynamic system is established with a focus on handling the trade-off of constraints on the heave and pitch acceleration, suspension deflections and tyre strokes. Actuator uncertainties are formulated within the controller design process and the fact of the actuator uncertainties existing in the system is modelled as a continuous-time homogeneous Markov process. A state feedback controller is designed for the purpose of ensuring that the resulting active suspension system is asymptotically stable with a prescribed H∞ disturbance attenuation level while simultaneously satisfying the constraint performance. The designed non-fragile H∞ controller is constructed via convex optimization by guaranteeing its sufficient condition in terms of feasible linear matrix inequalities. A half-vehicle case study is intensively exploited to reveal the effectiveness of the proposed controller design method.

Design of robust H∞ controller for a half-vehicle active suspension system with input delay

This article is concerned with the problem of robust H ∞ control for a half-vehicle active suspension system with input delay. The delay is assumed to be interval time-varying delay with unknown derivative. The vehicle front sprung mass and the rear unsprung mass are assumed to be varying due to vehicle load variation and may result in parameter uncertainties being modelled by polytopic uncertainty. First of all, regarding the heave and pitch accelerations as the optimisation objectives, and suspension deflection and relative tire load constraints as the output constraints, we build the corresponding suspension systems. Then, by constructing a novel Lyapunov functional involved with the lower and upper bounds of the delay, sufficient condition for the existence of robust H ∞ controller is given to ensure robust asymptotical stability of the closed-loop system and also guarantee the constrained performance. The condition can be converted into convex optimisation problem and verified easily by means of standard software. Finally, a design example is exploited to demonstrate the effectiveness of the proposed design method.

Sounding better: Fast audio cues increase walk speed in treadmill-mediated virtual rehabilitation environments

Music or sound effects are often used to enhance Virtual Environments, but it is not known how this audio may influence gait speed. This study investigated the influence of audio cue tempo on treadmill walking with and without visual flow. The walking speeds of 11 individuals were recorded during exposure to a range of audio cue rates. There was a significant effect of audio tempo without visual flow, with a 16% increase in walk speed with faster audio cue tempos. Audio with visual flow resulted in a smaller but still significant increase in walking speed (8%). The results suggest that the inclusion of faster rate audio cues may be of benefit in improving walk speed in virtual rehabilitation.

Multi-objective H∞ control for vehicle active suspension systems with random actuator delay

This article is concerned with the problem of multi-objective H ∞ control for vehicle active suspension systems with random actuator delay, which can be represented by signal probability distribution. First, the dynamical equations of a quarter-car suspension model are established for the control design purpose. Secondly, when taking into account vehicle performance requirements, namely, ride comfort, suspension deflection and the probability distributed actuator delay, we present the corresponding dynamic system, which will be transformed to the stochastic system for the problem of multi-objective H ∞ controller design. Third, based on the stochastic stability theory, the state feedback controller is proposed to render that the closed-loop system is exponentially stable in mean-square while simultaneously satisfying H ∞ performance and the output constraint requirement. The presented condition is expressed in the form of convex optimisation problems so that it can be efficiently solved via standard numerical software. Finally, a practical design example is given to demonstrate the effectiveness of the proposed method.

A study on half-vehicle active suspension control using sampled-data control

This paper is concerned with the problem of sampled-data H∞ control for a half-car active suspension system. First of all, by regarding the heave and the pitch accelerations, and the suspension deflection as the optimization objectives, the vehicle suspension system will be established. Then, an input delay approach is employed to transform the resulting active vehicle suspension system with sampling measurements into a continuous-time system with a delay in the state. Thirdly, by constructing a novel Lyapunov functional, a sufficient condition for the existence of sampled-data H∞ controller is given to ensure asymptotical stability of the closed-loop system and also satisfy the constraint performance. The corresponding condition can be converted into a convex optimization problem and verified easily by means of standard software. Finally, a design example is exploited to demonstrate the effectiveness of the proposed design method.

Visual properties of an object affect time to target in VR reaching tasks

Virtual Reality is being used increasingly for upper limb rehabilitation. The type of virtual objects used for reaching tasks varies widely, but there has been little work exploring the effect of different characteristics of objects on target acquisition time. This study investigates how target acquisition times vary for virtual objects with different visual cues. Results suggest that the visual properties of an object may have a notable effect on target acquisition times. Simple (low polygon) objects with richer depth cues are acquired more easily than a standard sphere.

Preliminary considerations for the computer analysis of fringe maps generated when holographic interferometry is applied as an NDT tool for airframe structures

The temptation when presented with the requirement to interpret holographic interferograms of aluminum aircraft structures derived through a non-destructive testing technique is to examine the whole interferogram. Computers are renowned for their ability to process large amounts of data accurately and speedily, therefore there is a strong temptation to harness their particular powers. This is not only time-consuming and wasteful of computing resources, it is also unnecessary. However, before work can begin on interpreting an interferogram by computer the problem itself must be defined. In this particular example the interferogram is from a sample taken from one of the worlds aging passenger airline fleet. The sample is from an aluminum stabilizer in which faults have been induced or have occurred during the service lifetime of the aircraft. All faults have been confirmed by destructive evaluation or by alternative techniques. Thus the problem domain is known. When a human expert examines an interferogram s/he concentrates on areas where faults are likely to occur namely, the areas immediately surrounding the stringers and frames as well as the stringers and frames themselves. The faults are typically caused through endless pressurization cycles or through corrosion. These faults have been induced to show themselves by a distinctive pattern of interference fringes across stringers and frames, where normally no fringes should be expected to occur. Therefore the human expert search concentrates on these areas, using the fringe count density or shape over the whole of the interferogram simply for comparison or control. The computer aims to emulate the human search. However, difficulties have been identified that could prove problematic for the computer that are elementary for the human brain. In our early work the sample interferograms for computer analysis have been selected because, to a human, they are uncomplicated and relatively noise-free sample in which faults are easily identified. This gives a good test case against which the computer can be compared, however the strength of the computer may finally by in interpreting holographic interferograms that are difficult for humans to interpret either though complexity or human consideration such as fatigue when hundreds either though complexity or human consideration such as fatigue when hundreds of such images are required where, for example, a large structure such as an aircraft is considered.