Deflection Input Research Articles

Analytical model of z-piezoelectric energy harvester for power generation from human physical activities

Human physical activities, viz., walking, jogging, jumping, etc on piezoelectric energy harvesters (PEH) have a great potential for the generation of free and clean energy. In the present work, an analytical model is developed to study the performance of a z-PEH, and the results were validated with numerical and experimental results. The distinctive features of the z-PEH are (a) it can be installed in a very small pavement/road surface area, (b) it results in very less damage to the road during installation, and (c) the repair and maintenance works can be carried out relatively easily. The power generation of the harvester can be enormously increased by increasing the number of unimorphs in the vertical (z) direction without increasing in the surface (x-y) directions, hence termed z-PEH. The harvester studied has four unimorphs. Each unimorph has a PZT-5A plate and an Aluminum substrate. The analytical and numerical studies resulted in a harvester with optimum dimensions for the PZT plate and Aluminum substrate of 20 × 20 × 0.4 mm3 and 65.1 × 20 × 1 mm3 respectively. Experiments were carried out on the optimum structure. The z-PEH, for an input deflection of 1 mm generated a maximum power of 0.84 mW, 0.88 mW and 0.80 mW from the proposed analytical model, numerical work and experiments respectively. The percentage of error between analytical and numerical results is 4.55% and between analytical and experimental results is 4.76%. An average human can generate a force of 490 N while walking, thereby allowing the use of 88 unimorphs in the z-PEH. From the analytical model, the resulted DC power of this harvester is 18.39 mW and the power density is 10.09 W m−3.

Experimental structural damage localization in beam structure using spatial continuous wavelet transform and mode shape curvature methods

Abstract An experimental dynamic vibration test using a non-contact scanning laser vibrometer is performed in order to extract the deflection shapes of two aluminium beams containing a notch cut out with a mill and two carbon/epoxy composite beams containing an impact damage of different severities. All of the beams are subjected to the clamped-clamped boundary conditions. These shapes are used as an input in a continuous wavelet transform technique for damage detection. In total, 78 wavelet functions with scale factors from 1 till 128 are used for the aluminium beams, whereas deflection shapes for composite beams are obtained in two dimensions, thus a two-dimensional wavelet transform is employed using 16 wavelet functions, all at scales from1 till 16. The scale, which is most suitable for damage identification, is found by calculating standardized damage index and the parameter called damage estimate reliability for the scales under investigation. Another method, based on mode shape curvature squares, is also applied to identify the damage. A baseline data of deflection shapes at a healthy state is not required for both methods to work. Damage identification results are compared for both methods. To assess the robustness of an algorithm involving both methods, different sensor densities are simulated by reducing the input deflection shapes by integer factors.

Real-Time Deflection Monitoring for Milling of a Thin-Walled Workpiece by Using PVDF Thin-Film Sensors with a Cantilevered Beam as a Case Study.

Thin-walled workpieces, such as aero-engine blisks and casings, are usually made of hard-to-cut materials. The wall thickness is very small and it is easy to deflect during milling process under dynamic cutting forces, leading to inaccurate workpiece dimensions and poor surface integrity. To understand the workpiece deflection behavior in a machining process, a new real-time nonintrusive method for deflection monitoring is presented, and a detailed analysis of workpiece deflection for different machining stages of the whole machining process is discussed. The thin-film polyvinylidene fluoride (PVDF) sensor is attached to the non-machining surface of the workpiece to copy the deflection excited by the dynamic cutting force. The relationship between the input deflection and the output voltage of the monitoring system is calibrated by testing. Monitored workpiece deflection results show that the workpiece experiences obvious vibration during the cutter entering the workpiece stage, and vibration during the machining process can be easily tracked by monitoring the deflection of the workpiece. During the cutter exiting the workpiece stage, the workpiece experiences forced vibration firstly, and free vibration exists until the amplitude reduces to zero after the cutter exits the workpiece. Machining results confirmed the suitability of the deflection monitoring system for machining thin-walled workpieces with the application of PVDF sensors.

Design and fabrication of a mems test socket with an attached tip for a ball-grid-array integrated circuit package

Microelectromechanical system (MEMS) test sockets with attached tips were developed for a ball-grid-array integrated circuit (BGA IC) package, using MEMS fabrication technology in conjunction with Ni-Co electroplating and XeF2 isotropic silicon etching. The electroplating process was used to create metal tips and thick metal cantilevers, which increased the contact reliability and conductivity. XeF2 isotropic silicon etching was used to release the cantilever array, which reduced the process cost and increased the mechanical stability. A finite element analysis (FEA) simulation was conducted to verify the force-deflection relationships of five types of cantilevers with attached tips. With an input deflection of 40 μm, the measured forces ranged from 12.55 to 26.14 mN, and matched the FEA results. The path resistance between a tip and the appropriate electrode pad was less than 3.49 Ω for all cantilevers when the tips were connected to the corresponding positions with more than 5 mN of contact force. The cantilever design with a length of 430 um and a tip height of 60 um (L430D60) showed the best performance in terms of the force-deflection relationship, a well as resistance. Therefore, the fabricated MEMS test sockets with tips are potentially applicable to actual BGA IC package tests.

Development of a flexure-based, force-sensing microgripper for micro-object manipulation

This paper presents the design and development of a flexure-based microgripper, accompanied with a real-time, vision-based force sensing system to handle objects of various sizes ranging from 100 µm to 1 mm. A simulation-based design methodology is adopted to develop an initial microgripper design, which is then optimized using theoretical modeling. The final prototype developed generated a large stroke length of over 500 µm with high-deflection magnification (ratio of the end deflection (output) to the input deflection) of 3.52. A spring system has been incorporated into the microgripper for easy measurement and control of the gripping forces. The web-camera-based visual system enables real-time force measurement with a resolution of 2.37 mN and can be operated in both manual and automatic modes to control the applied forces. The system has successfully demonstrated gripping of a variety of micro-objects including a 100 µm human hair and a 1 mm steel rod with forces as small as 43 mN and 159 mN, respectively.

Dynamic modeling of compliant constant-force compression mechanisms

A mathematical dynamic model is derived for compliant, constant-force compression mechanisms, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force compression mechanism (CFCM) is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully calibrated with empirical data from five separate mechanisms, comprising two basic configurations of CFCMs. The dynamic equation is derived from a generalized pseudo-rigid-body model. This allows every configuration to be represented by the same model, so a separate treatment is not required for each configuration. An unexpected dynamic trait of the constant-force mechanism is discovered. There exists a range of input deflection frequencies for which the output force of the mechanism is nearer to constant-force than it is with static input deflections.