Maple Toolbox for Switched Stabilizing Controller

This paper is celebrating the increment of interest in the application of  computer algebra in control system analysis. A Maple toolbox for stabilizing state feedback controllers for a class of switched system is presented. The attention is focused on finding the existence of common Lyapunov function  (CLFs), as this ensures stability for arbitrary switching sequences between several subsystems. The system considered here are restricted to second order linear  systems. In order to find the common Lyapunov function and the ability of the Maple software, the toolbox is proved to be less computational demanding compared to a lot of methods that has been solved by Linear Matrix Inequalities (LMI)

A Review Study for Robotic Exoskeletons Rehabilitation Devices

Nowadays, robotic exoskeletons demonstrated great abilities to replace traditional rehabilitation processes for activating neural abilities performed by physiotherapists. The main aim of this review study is to determine a state-of-the-art robotic exoskeleton that can be used for the rehabilitation of the lower limb of people who have mobile disabilities as a result of stroke and musculoskeletal conditions. The study presented the anatomy of the lower limb and the biomechanics of human gait to explain the mechanism of the limb, which helps in constructing a robotic exoskeleton. A state-of-the-art review of more than 100 articles related to robotic exoskeletons and their constructions, functionality, and rehabilitation capabilities are accurately implemented. Moreover, the study included a review of upper limb rehabilitation that has been studied locally and successfully applied to patients who exhibited significant improvements. Results of recent studies herald an abundant future for robotic exoskeletons used in the rehabilitation of the lower extremity. Significant improvement in the mechanism and design, as well as the quality, were observed. Also, impressive results were obtained from the performance when used by patients. This study concludes that working and improving the robotic devices continuously in accordance with the cases are necessary to be treated with the best results and the lowest cost

Generation of artificial road profile for automobile spring durability analysis

This paper presents the use of a generated artificial road profile in the simulation of a quarter car model for spring durability based-force extraction. In situ measurement of the road loading profile for automotive spring durability analysis, requires considerable cost and effort due to the complex experimental setup. Hence, an artificial road profile was generated for the quarter car model simulation to obtain the spring force signals. Initially, according to the ISO 8608 standard, a class “A” artificial road profile was generated using a designated waviness value, unevenness index and random phase angle. The generated road profile was used as the input to a constructed quarter car model to obtain the spring force signals. Subsequently, the generated nominal force signal was used to predict the fatigue life of the spring. Moreover, to obtain the localise fatigue behaviour of the spring, a finite element spring model together with the force signal was used for fatigue prediction. Under this class “A” road excitation, the spring possessed very high fatigue life of 1.87 × 106 blocks to failure. Further, a series of spring variant was analysed for fatigue life through this road class excitation. The relationship between spring stiffness and fatigue lives established using power regression and the coefficient of determination (R2) as high as 0.9815 was obtained. Therefore, this analysis will assist in automobile spring design regarding fatigue when road load data is not available

Research and modelling of surface roughness, cutting forces and I-kaz coefficients for S42C in turning using response surface methodology

This paper presents the optimization in machining processes on the cutting parameters for the S45C in turning process using the response surface method (RSM). The experimental work conducted investigates the influence of cutting parameters on statistical analysis of signals and surface quality. The paper also presents a statistical analysis of signal processing. The cutting force was measured during machining using the Kistler 9129AA dynamometer to monitor the force signals and the data was analyzed using the I-kazTM method of statistical analysis. This statistical analysis was used to assess the effect of force signals during the machining process. The RSM models for Ra and Rz, and I-kaz coefficients (Z) have been developed with ANOVA and multiple regression equations. The models also were compared and validated with the predicted and measured of Ra and Rz values, and I-kaz coefficients. The optimal configuration of cutting parameters was observed at 200 m/min, 0.1 mm/rev and 0.521 mm with desirability of 95.9%. It is observed that the models developed are suggested to be utilized for predicting surface roughness values and I-kaz coefficients for the machining of S45C steel

Preliminary study on the fabrication of aluminium foam through pressure assisted sintering dissolution process

This paper discusses the improvement made by pressure assisted sintering dissolution process (PASDP) as opposed to the solid-state sintering dissolution process (SSSDP) which was used in producing a much improved open celled aluminium foam. The improvements leads to an aluminium foam possessing a high dense of cell wall which is attainable in a much shorter time and possesses superior mechanical properties. By varying the local sodium chloride (NaCl) volume fractions in the sodium chloride/aluminium (NaCl/Al) compact, it is possible to fabricate aluminium foam with different relative densities. When subjected to monotonic compression mode, the fabricated aluminium foam exhibits typical stress–strain behaviour of metallic foam. The principles of Taguchi's Design of Experiments were employed to optimize processing factors for the fabrication of aluminium foam. Results were analysed based on Taguchi's signal to noise ratio (S/N) and analysis of variance (ANOVA) techniques in order to obtain the optimum combination of process parameter settings. Results indicate that the most notable factor influencing the fabrication of Al foam was the compaction at elevated temperature, followed by temperature, time and the process heating rate. The optimum processing parameters for the PASDP process were then predicted based on these results

Improving the Dynamic Characteristics of Body-in-White Structure Using Structural Optimization

The dynamic behavior of a body-in-white (BIW) structure has significant influence on the noise, vibration, and harshness (NVH) and crashworthiness of a car. Therefore, by improving the dynamic characteristics of BIW, problems and failures associated with resonance and fatigue can be prevented. The design objectives attempt to improve the existing torsion and bending modes by using structural optimization subjected to dynamic load without compromising other factors such as mass and stiffness of the structure. The natural frequency of the design was modified by identifying and reinforcing the structure at critical locations. These crucial points are first identified by topology optimization using mass and natural frequencies as the design variables. The individual components obtained from the analysis go through a size optimization step to find their target thickness of the structure. The thickness of affected regions of the components will be modified according to the analysis. The results of both optimization steps suggest several design modifications to achieve the target vibration specifications without compromising the stiffness of the structure. A method of combining both optimization approaches is proposed to improve the design modification process

Research of chatter suppression in turning operation with process damping using stability lobe diagram

This paper presents a chatter detection technique based on the stability of the measured Ra and Rz values of process damping and surface roughness in low cutting speed activities. In practice, process damping during machining procedures is hard to predict and identify due to the model and technique of limitation. The impact of cutting conditions on process damping in turning with P20 steel pre-hardened metal in terms of cutting velocity, feed rate and cutting depth was explored by the Stability Lobe Diagram method. A CNC turning machine was used in dry turning procedures with carbide insert. The highest and minimum value of natural frequencies and damping ratios were evaluated by modal testing and the stability lobe diagram analysis was applied. It is concluded that in the same region of the Stability Lobe Diagram, the chatter and measured surface roughness values were correlated and shown to have strong consensus

Analysis and design of classes of hybrid control systems

This thesis considers the problem of designing stabilizing controllers for hybrid systems. Generally speaking, the term hybrid systems refers to systems that exhibit interaction between continuous-time dynamics and logical events. The class of hybrid systems studied here are plants whose dynamics switch between several linear models. Control systems analysis and design is a non-trivial problem as established methods applicable to continuous-time and discrete-time systems cannot, in general, be extended to hybrid systems. This research focuses on two themes: the application of model reference adaptive control (MRAC) to hybrid systems and the stabilizeability of hybrid systems. In the first of these, we study the performance of output feedback against state feedback and free running against resettable adaptive control for single input single output (SISO) systems. Simulations reveal that output feedback and free running adaptive schemes are incapable of producing stabilizing control in some cases of hybrid systems.  Reset-table state feedback MRAC, implemented through a multiple model adaptive control structure, was found to provide very good results where the plant and reference outputs approached convergence, even in the presence of some perturbation. The problem of extending the method to multivariable hybrid systems is also investigated. Here, successful implementation of the scheme was found to depend on the decoupleability of both the plant and reference models. We propose guidelines on how this constraint may be overcome.  In the second theme, the objective was to identify the stabilizeability of hybrid systems through determination of the existence of control parameters such that all subsystems have a common Lyapunov function. Our work focussed on SISO switching systems with two continuous-time states. For systems modelled in continuous-time, we have derived a method from which this is achieved. A similar method for sampled-data systems has also been found, provided that all subsystems are modelled in the Brunovsky form</p

Vibration Analysis of Self-Healing Hybrid Composite Beam Under Moving Mass

In this study vibration analysis of hybrid epoxy composite beam under moving mass was investigated. Composite beam was reinforced unidirectional by carbon fibres and Shape Memory Alloy (SMA) wires. There is an open crack in the middle of the beam that is extended transversely in the beam structure and modelled as local flexibility. SMA fibres were embedded longitudinally in the layer of epoxy to heal the defected area by strain recovery. The Timoshenko beam model was used and the beam at the crack area was divided into two segments. Transfer Matrix Method (TMM) was then applied to solve the problem. Various volume fractions of wires in the epoxy were studied and found that, volume fraction of 2.5% can repair the defected beam as healthy one. It was observed that, using high volume fraction of SMA wires can significantly reduce deflection. Moreover, it was achieved SMA wires with volume fraction of 15% is capable to increase natural frequency of cracked beam 9.6%. Stress Intensity Factor (SIF) at the crack tip was studied and the recovery of the mode I SIF as a result of embedded wires revealed. The effect of various volume fractions of SMA wires, mass speed and crack depth were studied as well. There is a proper adjustment between the current results and those which were found through FEM

Stability of a Switched Linear System

Hybrid systems are dynamic systems that arise out of the interaction of continuous state dynamics and discrete state dynamics. Switched systems, which are a type of hybrid system, have been given much attention by control systems research over the past decade. Problems with the controllability, observability, converseability and stabilizability of switched systems have always been discussed. In this paper, the trend in research regarding the stability of switched systems will be investigated. Then the variety of methods that have been discovered by researchers for stabilizing switched linear systems with arbitrary switching will be discussed in detail