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ABSTRACT: Describes an integrated approach to design and fabricate scaffold/cell constructs for tissue engineering. With this approach it becomes possible to produce scaffolds with controlled distribution of living cells and growth factors, a critical condition for successful grafting. Our idea consists of building a scaffold/cell construct by robotic micro-assembly of microscopic polymer building blocks. The paper introduces the rationale and concept of this interdisciplinary project and presents some realized steps. A 3D contact FEM simulation has been carried out to study the forces involved on the scaffold elements and micro-gripper during assembly. An error analysis has been performed to evaluate the accumulated error when building a scaffold/cell construct. A dedicated monolithic shape memory alloy micro-gripper has been realized and tested, which is able to handle parts in the range of 50-100 microns.
Robotics and Automation, 2002. Proceedings. ICRA '02. IEEE International Conference on; 02/2002
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ABSTRACT: In micro-robotics and for micro-systems, one cannot simply scale down conventional actuators. Specific difficulties like friction forces between parts and the assembly have to be considered carefully and need a special design strategy adapted to this “micro-world”. Shape Memory Alloys (SMA) have strong potential in micro actuators. So far, most of SMA devices used the SMA material as a part of a mechanical system, which raised several problems when scaling down. In this paper, a concept of monolithic SMA micro-devices, which consists in considering the SMA as a mechanical system by itself, is presented. Several applications are shown to illustrate this concept.
MRS Proceedings. 12/1998; 604.
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R. Clavel,
P. Helmer,
S. Bottinelli,
S. Henein,
C. Schmitt,
R. Perez,
A. Bergander,
J.-M. Breguet, Y. Bellouard,
H. Langen,
P. Rouiller,
C. Baur,
Y. Mabillard
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ABSTRACT: The concept of monolithic shape memory alloys (SMA) micro-devices is to integrate all device functions within the same piece of material. This is very interesting in the field of micro-systems, because assembly is avoided. In such devices, the main problem is to create a reversible motion. Recently, the use of the two-way shape memory effect has been investigated. A simpler solution could be to integrate a pullback spring within the monolithic structure. This implies introducing shape memory properties only in some predefined parts of the material. In this paper, an approach based on local annealing of the material is proposed. The annealed parts will exhibit a shape memory effect and the remaining non-annealed parts will have an elastic behavior. Two methods of local annealing have been investigated. The first one is done by an electrical current, which needs a special design of the electrical path. The second one is done by local laser heating, which allows complete freedom in choosing the ‘memory regions’ of the material. With these tools, complex mechanical devices with active and passive parts can be designed. To illustrate this idea, two mechanical structures containing locally annealed parts are presented.
Materials Science and Engineering: A.
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ABSTRACT: This paper presents a monolithic shape memory alloy (SMA) microgripper, which was developed to assemble microscopic building blocks of width 60 μm into tissue engineering scaffolds. It consists of two small fingers for grasping, an actuator which changes its shape upon heating by Joule effect and a parallel elastic structure to provide a pullback force on cooling as well as to guide the finger movement. All the elements are laser-cut from the same Ni-Ti-Cu sheet but have different mechanical properties and are used for different functions. Using local laser annealing, a local shape memory effect is introduced on the actuator while leaving other areas in a cold-worked state, i.e. no shape memory effect occurs. The material has nonlinear mechanics and the actuator undergoes large deflections. A numerical method is introduced to compute the nonlinear dynamics of the coupled system formed by the actuator and pullback spring. The predicted deflection and force are in good agreement with the measured ones, and this model can be used to optimize the design.
Robotics and Automation, 2004. Proceedings. ICRA '04. 2004 IEEE International Conference on;
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ABSTRACT: A complete set-up for local annealing of Shape Memory Alloys (SMA) is proposed. Such alloys, when plastically deformed at a given low temperature, have the ability to recover a previously memorised shape simply by heating up to a higher temperature. They find more and more applications in the fields of robotics and micro engineering. There is a tremendous advantage in using local annealing because this process can produce monolithic parts, which have different mechanical behavior at different location of the same body. Using this approach, it is possible to integrate all the functionality of a device within one piece of material. The set-up is based on a 2W-laser diode emitting at 805nm and a scanner head. The laser beam is coupled into an optical fiber of 60 mum in diameter. The fiber output is focused on the SMA work-piece using a relay lens system with a 1:1 magnification, resulting in a spot diameter of 60 mum. An imaging system is used to control the position of the laser spot on the sample. In order to displace the spot on the surface a tip/tilt laser scanner is used. The scanner is positioned in a pre-objective configuration and allows a scan field size of more than 10 x 10 mm(2). A graphical user interface of the scan field allows the user to quickly set up marks and alter their placement and power density. This is achieved by computer controlling X and Y positions of the scanner as well as the laser diode power. A SMA micro-gripper with a surface area less than 1 mm(2) and an opening of the jaws of 200 mum has been realised using this set-up. It is electrically actuated and a controlled force of 16mN can be applied to hold and release small objects such as graded index micro-lenses at a cycle time of typically 1s.
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ABSTRACT: Most of Shape Memory Alloy (SMA) devices use only the SMA material as the actuating part or in some cases as the flexible part of the device (superelastic hinges). Commonly, simple wires, strips or springs are used for the actuating part. All these systems need an assembly procedure which raises several problems in the micro-system field : careful assembly, sometimes friction, .... The concept of monolithic SMA micro-devices presented in this paper is to integrate all functions of the device within the same material. For example, in a micro-gripper, the jaws and the moving part are made out of the same piece of material. With this technology, we avoid any assembly in the small dimensions. Moreover sub-millimeter devices can easily be designed and further miniaturization can be achieved. As an illustration, two micro-devices based on this concept are presented.
http://dx.doi.org/10.1051/jp4:1997595.
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ABSTRACT: The Two-Way Shape Memory Effect (TWSME) has been widely studied in the literature. However, little attention has been paid about the out-of-equilibrium behavior of the TWSME. This paper reports some experiments, which were performed on specimens, previously trained in bending according a constrained temperature cycling process. Once the training process was done, specimens were deformed in their martensitic state such as a permanent deformation remains. In other words, specimens were set in a position that is out their stable path previously introduced by the TWSME procedure. By heating up, samples recover their original shape, thus clearing the effect of the perturbation. However, the transformation back to the stable cycle exhibits some unusual behavior. For instance, the shape change starts at a temperature well below the material transformation temperatures. Considering the macroscopic motion of the specimen, a two-step motion is observed. While heating, the material changes its shape, going back to the TWSME-induced martensitic shape, until the martensite-to-austenite transformation temperature is reached after what the specimen follows the original trained path and transforms to the austenite shape. This two-step transformation is thoroughly described in this paper.
http://dx.doi.org/10.1051/jp4:2003994.
