Christine Prelle

A Four-Discrete-Position Electromagnetic Actuator: Modeling and Experimentation

In this paper, an electromagnetic actuator having four discrete positions is discussed. The principle, the modeling, and an experimental device of this actuator are presented in this study. This actuator is composed of a mobile permanent magnet, four fixed permanent magnets, which ensure the holding of the discrete positions, and two perpendicular wires to switch independently in two perpendicular directions. The mobile part has four discrete positions, two in each direction. An electromagnetic actuator modeling has been realized to compute the magnetic and electromagnetic forces exerted on the mobile magnet and its displacement. The experimental device was designed using this model and then manufactured. The stroke of the mobile part is 1 mm times 1 mm. The driving current ranges from 3 to 7 A. A comparison between experimental and modeled results is carried out. Good agreement on the displacement curves and on the rise times is observed for all the range of controlling currents.

Development of a Control Module for a Digital Electromagnetic Actuators Array

In this paper, a digital actuators array composed of 25 elementary digital actuators placed in a 5 × 5 matrix configuration is presented. The originality of the elementary digital actuator lies in its ability to reach four discrete positions in a horizontal xy-plane. An analytical model of the array is presented and has been used to design an experimental prototype. A control module is proposed to independently or simultaneously control the elementary actuators along two displacement axes. This module is based on a control strategy and on a dedicated electrical control circuit which reduces the number of channels needed to control the array. The proposed control strategy is based on position and displacement matrices to characterize the desired motion of each elementary actuator. Experimental tests of the actuators array are presented in the paper to validate the control module. Finally, an application of the array as a xy-plane displacement device is shown.

Wavelength-Selective Shape Memory Alloy for Wireless Microactuation of a Bistable Curved Beam

Wireless and/or sensorless components offer a great potential for friendly integration in mechatronic systems. This paper presents a wireless technique to actuate a bistable curved beam using wavelength-selective shape-memory-alloy (SMA) thin foils. The SMA thin foil is irradiated remotely by continuous-mode laser diodes of 785 and 658 nm wavelengths. First, a comparison between two numerical thermal models is done. These models obey the same conduction and convection equations but the effect of phase transformation is integrated in two different ways. A good agreement is found between the two simulation results. Then, the force generated by the SMA sample (size: 3 mm × 1 mm × 0.1 mm), during martensite-to-austenite phase transformation, is experimentally measured using a miniature force sensor. The force comes out to be 403 mN with 70 mW laser power. Using this force value, a bistable curved beam is designed and fabricated by rapid prototyping technique. Optical filtering layers, which are responsible for the wavelength-selective response, are directly deposited onto the SMA samples. Finally, two SMA samples are used to switch the curved beam between its two stable positions.

Wavelength Dependent Remote Power Supply for Shape Memory Alloy

The use of shape memory alloy (SMA) actuators in smart structures is increasing significantly especially in the field of Micro-Electro-Mechanical Systems (MEMS) due to their unique properties. In this work wavelength dependent remote power supply for SMA is presented to avoid electrical cables from the working area of the structure and to demonstrate the selective addressing of a high number of micro-actuators placed in a small space. Low power (∼100 mW) continuous mode laser diodes are used as remote power supply sources. A thermal numerical model is presented to visualize the temperature evolution in a Nitinol sample (3 mm × 1 mm × 100 μm) irradiated by 785 nm laser source. A series of experiments are performed to validate the modelling results, to estimate the response time under different loadings (15 g and 20 g) and to demonstrate the wavelength dependent deformation in SMA samples for selective addressing which is realized by depositing thin layers having specific optical filtering properties directly over the SMA sample and using laser diode sources with different wavelengths (785 nm and 658 nm).

A planar electromagnetic actuator based on two layer coil assembly for micro applications

In this paper, the concept of a two layer coil based electromagnetic actuator for planar motions is presented. The actuator is composed of two pairs of fixed overlapped 2D electric drive coils and a mobile part consists of permanent magnets arrays which perform motions in xy plane due to the generation of Lorentz force. A multi-layer printed circuit board is used for the two layers of drive coils. An electromagnetic model of the actuator has been developed in order to compute the electromagnetic force exerted on the magnets arrays. A prototype of the device has been manufactured and tested. The mobile part displacement along the two displacement axes have been shown and determined using image processing method.

Contactless and selective energy transfer to a bistable micro-actuator using laser heated shape memory alloy

Contactless energy transfer (CET) methods offer great flexibility in the design of complex micro-systems. This paper reports a laser based contactless and selective energy transfer method. A compliant bistable micro-actuator (curved beam of size 25 mm × 1.5 mm × 0.508 mm) is actuated between its two stable positions using the laser heated shape memory alloy (SMA) active elements (size: 3 mm × 1 mm × 0.1 mm). The switching time of the actuator turns out to be 0.5 s for d0 equal to 700 μm and a laser power of 90 mW (d0 is half of the total stroke length). The paper also demonstrates the selective energy transfer technique to the SMA active elements by depositing silver based optical filters directly onto the SMA active elements. A successful demonstration is presented for four wavelengths, 532, 660, 785, and 980 nm, using different values of d0 for the bistable micro-actuator. Finally, a long-term test is performed to highlight the thermo-mechanical effect on the selective addressing capability of the optical filters.

Silicon conveyor based planar electromagnetic device for linear displacement

In this work a planar electromagnetic motion device is presented for linear displacement. The motion forces are generated by the interaction between the currents in planar electrical drive coil, placed beneath the adjacently inverted magnets array with an insulating glass layer of 170 µm thickness in between. To achieve linear displacement in a plane, four adjacently inverted magnets arrays are assembled orthogonally to a micro-fabricated silicon cross structure and four planar electrical drive coils are assembled in an aluminum platform. The first prototype of this planar device is able to perform linear displacement in XY-plane with a positional repeatability error of 2.54 µm and 1.32 µm along X- and Y-axis respectively. The device is able to perform in free and self guided mode with a straightness error of 15.13 ± 5.64 µm and 3.02 ± 1.69 µm respectively.

Nitinol thin foil irradiated by continuous mode laser diode for wireless chromatic micro-actuation

In this article a method for wireless micro-actuation based on shape memory alloy (SMA) is investigated. First of all, a numerical model is presented having conduction and convection heat transfer modules and the effect of phase transformation is taken into account during heating and cooling of SMA. The numerical simulation is performed using Cast3M code and the physical properties of Nitinol (which is an alloy of nickel and titanium) irradiated by a continuous mode laser diode of wavelength 785 nm and optical power equal to 102 mW. An experimental work is carried out to validate the numerical modelling. For this purpose a square sample of Nitinol (2mm × 2mm × 100µm thick) is irradiated with the laser source and the temperature rise within the sample is measured using miniature thermocouples. A good agreement is found between the experimental and numerical results. At the end, the chromatic response of Nitinol thin foils using Bragg reflector structure is presented.

Optimized design of a four discrete positions electromagnetic actuator

A four discrete positions electromagnetic actuator was designed, manufactured and tested. The design was optimized in performances and size. This actuator is composed of a mobile permanent magnet, four fixed permanent magnets and two orthogonal wires. Each wire is used to switch independently in two orthogonal directions. The displacement of the mobile magnet is limited by two stops in each direction. The mobile part can then reach four discrete positions. The fixed permanent magnets ensure a holding of each discrete position. This paper presents the principle, the optimized design, the modelling, an experimental device and experimental results of this actuator.

Bistable curved-beam actuated by optically controlled Shape Memory Alloy

In this work, a bistable curved-beam is actuated between its two stable states using the force generated by optically controlled SMA elements. Two Shape Memory Alloy (SMA) elements are used for this purpose forming an antagonistic pair. Two laser sources (wavelength equals to 785 nm and 658 nm) are used to heat the SMA active elements in order to induce the martensite to austenite phase transformation in the SMA. The force generated by the SMA sample (3 mm × 1 mm × 100 μm) is measured experimentally using a miniature force sensor which comes out to be 706 mN for 100 mW laser power value. The bistable curved-beam is designed according to these force measurements. At the end, experimental demonstration of the proposed actuation technique is presented.