Zaidi Mohd Ripin

Development of a low-cost modular pole climbing robot

This article reports on the design and development work on a modular pole climbing robot. Modularity was achieved by ensuring similar repeated structures can be coupled and controlled in almost similar fashion. The design considers the rudimentary aspect of climbing and adopts grasp-push-grasp motion arrangement. The resulting design consists of two grippers for grasping and two central arms for climbing and lowering, all of which employs pneumatic cylinders. The whole climbing motion was achieved in six steps and the climbing speed is determined from the rate of filling the pneumatic cylinders involved. Parallel four-bar linkages arrangement was used to ensure the horizontal orientation of the grippers to prevent locking. The structure of the robot are made from aluminum with pin joints throughout to allow for easy assembly. PLC was used at this stage for the motion control. The developed robot can climb a 150 mm diameter pole at a speed of 0.6 m/min.

Numerical simulation of sheet stamping process using flexible punch

Abstract Different from the conventional stamping process, rubber forming uses a rubber pad contained in a rigid box to act as a punch. The main attraction of the process is its simplicity, and it can be used for prototype development or for low-volume production. In this study, an axisymmetric rubber-pad forming operation is investigated via numerical simulations and experiments. Some key process parameters, such as rubber material, hardness of flexible punch, stamping velocity, rubber-pad thickness, and friction are studied in detail. Good correlation is achieved between the finite element predicted and experimentally measured thickness—thinning in the formed part. Stress and strain distributions in the specimen are investigated numerically during the process using ABAQUS/Standard.

Optimization of an engine mounting system with consideration of frequency-dependent stiffness and loss factor

An engine mounting system is the primary vibration isolator of the engine from the chassis. The frequency-dependent stiffness and loss factor present a more accurate representation of a rubber mount as opposed to the frequency-independent damping model. In this article, dynamic optimization of an engine mounting system considering the frequency-dependent stiffness and loss factor is presented. The dynamic properties in all three principal directions are measured on the basis of the optimum locations and orientation angles of the individual engine mounts, which are identified to minimize the mean force transmissibility of the system for a range of frequencies, resulting in a 45% reduction in the vertical transmissibility to the installation base. In comparison, optimization based on a frequency-independent stiffness underestimated the peak transmissibility, and minimization of the vertical force transmissibility created a significant increase in other directions. The optimum parameters are applied to a small utility two-stroke engine. A significant reduction in the transmitted force and engine displacement is demonstrated.

Analysis of Surface Parameters and Vibration of Roller Bearing

The surface of the inner race of a detachable roller bearing is monitored periodically to determine the deterioration pattern under normal conditions together with the vibration level. The surface of the inner race is scanned using an infinite focus microscope to evaluate surface properties utilizing the 2D and 3D parameters. Both parameters successfully assess the surface degradation and wear of the bearing surface. Using the Dowson-Higginson equation on elastohydrodynamic lubrication, the theoretical lubrication film was calculated and the lubrication regimes identified. A high vibration level can be associated with surface roughness properties and relative lubrication regime. This work highlights the relationship between the bearing vibration level and the bearing inner race surface parameters. The two surface parameters with the highest Pearson correlation coefficient with the vibration level are the areal surface roughness Sa (0.997) and the average roughness Ra (0.936).

Predicting combined-cycle natural gas power plant emissions by using artificial neural networks

Gaseous emission from a chimney is recognized as one of the sources of pollution produced from a typical power plant. Among the pollutants of concern from the chimney of the power plant are NO/sub x/, SO/sub 2/ and CO. Commonly, the application of continuous emission monitoring systems (CEMS) is used to measure the emissions directly. It is possible however, to predict stack gases from the combustion chamber indirectly so that a build up of a database on related input and output of various parameters can be generated. From this relationship, the critical points of various parameters can be optimized to limit the pollution from the chimney. An artificial neural networks (ANN) based on a feedforward backpropagation model is selected for this objective. The limited data taken from Lumut Power Plant are used to train the neural network. This prediction from neural network based on training agrees well with the data taken from CEMS.

The operational deflection shapes and transient analysis of the brake shoes in drum brake squeal

The operational deflection shapes were used to identify the mode of vibration for the brake shoes in drum brake squeal. The measurement of the operational deflection shapes of the brake shoes during drum brake squeal, which was in the torsional mode, was similar to that of the modes obtained from the experimental modal analysis of the brake shoes under the in-contact static condition. A two-degree-of-freedom model was developed on the basis of the experimental modal analysis data within the limited bandwidth of the squeal frequency of 1850 Hz. In this work, the operational deflection shape was used for determination of a structural dynamic modification to be carried out on the brake shoes in order to maximize the damping of the torsional mode as a way to improve the stability of the system. The lumped-parameter model was then used to assess the effect of the structural dynamic modification on the squeal based on the transient analysis, which showed a similar trend and can assist brake designers in evaluating the critical parameter to obtain a squeal-free drum brake design.

Modeling of Microindentation with Consideration of the Surface Roughness

A finite element model of a microindentation is developed where the scanned surface topography data which represent the actual surface-roughness values are used in the construction of the finite element model of the workpiece. Indentation simulation with friction effect solely due to the surface deformation produces results which match the experimental ones in terms of residual indent size and pile-up heights. A roughness-dependent friction model is developed, which is comparable with the models proposed by Johnson (1985) and Alcála (2004).

High strain-rate bulge forming of sheet metals using a solid bulging medium

Abstract The biaxial bulge-forming of sheet metals is a standard test to evaluate the formability and mechanical behaviour of materials. A new dynamic bulge-testing method is simulated and analysed in this study that can be performed on a conventional split Hopkinson pressure bar (SHPB) system. The aim of this work is to develop a numerical and theoretical technique for the analysis of materials and structures, which are dynamically loaded and subjected to the different levels of strain rates. The commercial finite element code ABAQUS/Explicit has been selected as the numerical test bed for the simulation of the dynamic bulging test. In the new bulge-forming technique, flexible rubber is used as the pressure-carrying medium instead of hydraulic fluid. The theoretical analysis is based on conventional hydraulic bulge test principles and SHPB relations. To verify the accuracy of the developed technique, analytical and finite element methods are compared and show good correlation with each other.

The effective frequency range of an active suspended handle based on the saturation effects of a piezo stack actuator

This paper presents a novel approach to the design of an active suspended handle by identifying the effective frequency range, based on the saturation effects of the piezo stack actuator, in terms of the force-displacement-voltage relationship as a function of the excitation frequency. The effective range allows for proper matching between the operating speed of the machine and the suspended handle. A model of the active suspended handle was developed, which took into account the non-linear saturation effect of the piezo stack actuator. A proportional-integral-derivative controller generated the counter voltage for the piezo stack actuator, using a proportional feedback gain (P) step up method, in order to attenuate the vibration transmitted to the handle. By including the saturation effect, the Pearson’s correlation coefficient (R2) of the model improved to 0.97, within the frequency range of 50 ∼ 500 Hz. Using this approach, we identified that the effective frequency range of isolation with transmissibi...This paper presents a novel approach to the design of an active suspended handle by identifying the effective frequency range, based on the saturation effects of the piezo stack actuator, in terms of the force-displacement-voltage relationship as a function of the excitation frequency. The effective range allows for proper matching between the operating speed of the machine and the suspended handle. A model of the active suspended handle was developed, which took into account the non-linear saturation effect of the piezo stack actuator. A proportional-integral-derivative controller generated the counter voltage for the piezo stack actuator, using a proportional feedback gain (P) step up method, in order to attenuate the vibration transmitted to the handle. By including the saturation effect, the Pearson’s correlation coefficient (R2) of the model improved to 0.97, within the frequency range of 50 ∼ 500 Hz. Using this approach, we identified that the effective frequency range of isolation with transmissibility less than unity is between 250 ∼ 450 Hz. The active suspended handle was attached to a die grinder with a nominal operating speed of 25000 rpm and the vibration transmitted from the die grinder to the handle was reduced by 91%.

Structural dynamic modification of an active suspended handle with a parallel coupled piezo stack actuator

This article presents the structural dynamic modification technique, applied to an active suspended handle, to overcome the displacement limitation of a piezo stack actuator by increasing the stiffness of the lower beam of the handle that supports the piezo stack actuator. The increased stiffness shifted the modes of the structure beyond the operating frequency range. The structural dynamic modification model with linearized piezo stack actuator hysteresis showed better performance compared to the original-active suspended handle model. A proportional feedback gain (P) step-up method is used for counter voltage to the piezo stack actuator in a real-time active vibration control system. The effective frequency range of isolation, with transmissibility smaller than unity, was expanded from 250–450 Hz to 200–510 Hz, and the anti-node transmissibility was lowered from 218 to 226 dB. Laboratory testing using a die grinder with a nominal operating speed of 25,000 r/min showed that the structural dynamic modification-active suspended handle reduced vibration transmissibility by up to 96%.