Yoan Civet

Optimal design of a squeeze film actuator for friction feedback

Sense of touch belongs to one of the five Human Senses. Whereas blind people largely use feeling in everyday life, sighted person mainly focus on hearing and vision. However, haptic interface started being introduced in customers applications, such as smartphone, to propose new opportunities to users. A surface put in vibration nearby another can modify the friction coefficient measured between the two objects. This is known as the squeeze film effect. The aim of this paper is to present the optimization of a piezoelectric actuator for friction feedback. Since the computation of the Squeeze film Finite Element (FE) model is time-consuming, it is also proposed to focus only on the mechanical simulations. Indeed, a correlation between the force of the actuator and the volume swept by the travel of the vibrating surface is brought out. Finally, a couple of optimization results are presented for different topologies of actuators.

Bingham-Papanastasiou and Approximate Parallel Models Comparison for the Design of Magneto-Rheological Valves

Magneto-Rheological Fluids (MRFs) are smart materials whose physical properties can be controlled by an exciting magnetic field. MRFs are described as Bingham plastics with variable magnetic field dependent yield stress. Thanks to their particular features, MRFs have been largely employed to realize controllable power dissipating devices and, among them, regulable valves without moving parts. The most commonly configuration used for MRF based valves consists on fluid flow through an annular duct. The conception of such valves implies to deal with different physics. In particular, the magnetic circuit is usually designed and verified by mean of FE (Finite Element) analysis, while the duct geometry is usually dimensioned using an approximated formula based on fluid flow between parallel plates. In the presented work, a complete and detailed derivation of the analytical model is discussed in order to describe the flow of MRFs through an annulus using an approximate parallel plate geometry. Successively, the Bingham-Papanastasiou regularization is chosen as the mean to accurately describe the continuous non-linear yield stress and shear dependent viscosity of a commercially available MRF and it is then implemented into a FE software. This step allows to built a complete multiphysics problem for the design of MRFs based devices. Results obtained from the analytical model and FE analysis are then compared and the different steps in the proposed approaches are validated.

Design and modelling of a test bench to characterise magnetic fluids

The proposed paper discusses a set-up to monitor the B-H curve of magnetic fluids, which have low permeability. An analytical model confronted to FE simulations is investigated in order to design the targeted set-up. A second modelling is evaluated to obtain the flux density of the characterised fluid, knowing the input current from the primary coil and the induced voltage in the secondary coil. Couple of measurements are performed to validate the final set-up and the methodology.

A novel electronically-controlled linear escapement mechanism

The linear escapement mechanism presented in this paper has been developed to assist in a task where a large thrust force (>10 N) is required with a high positioning resolution (<;0.5 mm) in a battery-powered device. This paper describes the behaviour of the escapement, the design process, based on the dynamic modelling of the output, and the sizing of the key features with a view towards miniaturisation. A prototype is used to validate the design options.

Design considerations for a contactless battery charger

Contactless power transfer using inductive coupling is a well-known way to transfer energy from a transmitter to a receiver without any physical link. The applications are multiple. In this paper, the design and control of such a system for a contactless battery charger is investigated. The behaviour of the battery turns the system into a non-linear one. A solution dealing with the compensation topologies which aims to simplify the control of the transformer without any additional power electronics is proposed.

Modeling and characterization of a MEMS synchronous generator

This paper addresses the modeling of a three-phase electromagnetic MEMS generator. First, the differential non-linear equations that govern the electrical and mechanical dynamics are derived. An existing device is taken as a case study, and different strategies (analytical calculation, FE analysis or direct measurement) are used in order to obtain its characteristic parameters, which are then introduced into the model. Finally, the system is simulated under different operating conditions, and the results are compared to the measurements. The experimental data are in good agreement with the theoretical predictions (discrepancy below 6%).

Modelling and design of complex geometry parts vibratory conveying

As one important component in automatic assembly, the vibratory parts feeder needs to be designed more efficiently. A widely used analytical model to study the vibratory conveying mechanics of parts feeder is the bouncing ball model. However this latter is only suitable for simple parts. In this paper, 3D simulations with SolidWorks™ software is performed to model complex geometry parts. At first, the bouncing ball system is simulated with SolidWorks™ to validate the 3D simulations. The consistency between 3D simulations and bouncing ball analytical model insures the feasibility to apply 3D simulations for complex geometry parts. Then the simulations are used for nuts and corresponding experiments are carried out. The consistency between the experiments and simulations assures that this 3D simulation can be used to predict the complex geometry parts behaviour under different vibrating frequencies and amplitudes, and thus to improve parts feeder design.

Equivalent piezoelectric actuator circuits and comparison

Equivalent piezoelectric actuator circuit is necessary for certain applications. Previous models have limits and are not accurate on modelling the real part of piezo impedance at low frequency range. A simple inverse proportional to frequency model is proposed and experimentally validated. The comparison with other models show also it is the most robust model.

Improved analytical model of hyperelastic magnetic membrane

This paper proposes an analysis of multi-factor fabrications of magnetic membranes. In order to acquire some knowledge about the influence of fabrication factors, an analysis is performed using a Design of Experiment (DoE) methodology. The latter is applied on the mechanical model (Yeoh model), which describes the deformation of the magnetic membranes; specifically, the influence of the fabrication factors on the constants of the Yeoh model.

Energy analysis of a DEAP based cylindrical actuator coupled with a radial negative stiffness spring

The main problem to obtain considerable deformation with dielectric electro-active polymer based technology is the electrical breakdown. A simple solution consists in pre-stretching the elastomer before activating it which cancels the snap-through effect and thus avoid reaching the electrical limit. Due to the stress characteristic of the DEAP, it could be demonstrated that a spring with a negative stiffness provides the best strain. In this paper, a new design of a monostable spring with a negative stiffness is suggested for a DEAP tubular shape actuator. The particularity of the proposed solution is the radial direction of the displacement with a special load characteristic. In order to determine the performance of the system, the mechanical and electrical behaviour are investigated through analytical models with the assumption that the axial stretch stays constant. A finite element method is used to validate these latter and maximal error lower than 2% is reported. The energy chain conversion is developed in detail which allows studying all the energies transferred from both the electrical input and any pre-stretch solution to the membrane during a cycle of activation. From these models, the negative stiffness spring is compared to the common solution, i.e a constant pressure or a linear positive spring, to pre-stretch a cylindrical EAP. The results show that the linear spring always removes the snap-through behaviour contrary to the constant pressure. Depending on the geometry, the monostable solution cancels also this latter and owns a better energy transfer from the power supply to the elastomer (around 50% against 40% for the linear spring) or a better stroke compared to the linear spring. Furthermore, due to the hollow in its stress characteristic, the cylindrical shaped actuator associated to a linear spring or the proposed spring allows increasing the strain. Through the different analytical models, the definition of the electrical breakdown and the analysis of the limits of the stresses, a qualitative study of the performance is given for the different pre-stretches.