Design of a 3 DOF displacement stage based on ferrofluids.

International audienceThis paper presents the design of a 3 DOF (Degrees Of Freedom) displacement stage. This stage is composed of a mobile platform in suspension on three ferrofluid bubbles as an hydrostatic suspension. Bubbles stay attached to the platform thanks to three permanent magnets fixed on this platform. The actuation is obtained by fixing and controlling three coils on the support near the magnets. The dynamical characteristics of the stage are tuning by choosing appropriate volumes and properties for the ferrofluid and permanent magnets. The control in open loop permits a resolution of 50 nm but unfortunately a lower repeatability. The stage will be improved in the future by using a position feedback control

Modeling, Identification and Control of a Thermal glue based temporary fixing system : Application to the Micro-Robotic field.

International audienceThe purpose of this paper is to present a temporary fixing system based on a thermal glue that is well-adapted to micro-robotics. In the paper, ths system is used to design a tool changer but can be generalized to other micro-robotic applications. A thermal modeling and an identification procedure are presented to propose a strategy to control the system. This system takes place into a micromanipulation station to gain flexibility, space and complexity. Indeed, to perform sequences of micromanipulation tasks (i.e. micro-assembly sequences), only one manipulator, able to use sequentially several end-effectors, has to be used instead of several dedicated to one specific task

Flexible micro-assembly system equiped with an automated tool changer.

International audienceThis paper deals with the design, fabrication and experimental validation of several modules of a micro-assembly system. On one hand, a microgripper is integrated in a four degrees of freedom system. On the other hand, a tool changer is designed. It enables to exchange automatically the tip part of the microgripper and then dedicated tools can be used to achieve specific tasks. The principle of this tool changer relies on a thermal glue whose phase (liquid or solid) is controlled by heat generators. This system is based on the modeling of thermal phenomena in the tools during a cycle of tool exchange. A compliant system is added to limit micromanipulation forces applied during assembly tasks like insertions. Finally, the successful assembly of several microcomponents is detailed, highlighting the capabilities and benefits of the whole system

Temporary fixing systems for applications in Microrobotics.

International audienceThis paper focuses on temporary fixing systems for microrobotics. Several solutions from the art are presented and compared : solutions based on mechanical bending, electromagnetic elements, electrostatic forces, glues, polymers or Van der Waals forces. From this analysis, we designed and developed a new system based on thermal glue (that permits to exchange the tip part of a microgripper) for microassembly stations. This system brings a high flexibility and compactness for microrobotic applications

Port hamiltonian modeling of MSMA based actuator: toward a thermodynamically consistent formulation.

International audienceThis paper presents a thermodynamically consistent model of MSMA (Magnetic Shape Memory Alloys) under port Hamiltonian framework. It is based on previous works on MSMA proposed in (Gauthier et al., 2008; Calchand et al., 2011). The main di erence lies in the choice of the state variables and manipulated thermodynamic forces. Furthermore in (Gauthier et al., 2008), subsequent experiments revealed a highly hysteretic behavior of these materials. Here, the simpli ed hysteretic behavior is incorporated into the port-hamiltonian model to obtain a ner and more precise model. Such modeling will allow the use of a wide range of energy based methods to design the associated control system. The paper ends with some extensions to more complex hysterestic phenomena by using Preisach like model. First ideas are proposed to extend the previous physical model to systems with internal hysteretic loops

Multi-axis Force Sensing with Pre-stressed Resonant Composite Plates : An Alternative to Strain Gauge Force Sensors

International audienceIndustrial robots embedding multi-axis force sensors at the robot/environment interface presents numerous advantages in terms of safety, dexterity and collaborative perspectives. The key-point of these developments remains the availability of cheap but sufficiently precise multi-axis force sensors. This paper proposes a model-based approach to design a new alternative to commonly used strain gauge sensors. The principle of the device relies on pre-stress resonant composite plates where feedback control and measurement are achieved with piezoelectric transducers. The main originality of this work is that the force to be measured may present multi-axis components. Based on pre-stress and piezoelectric theories, a complete electromechanical model is proposed. This one is used during the design of a resonating composite Mindlin plate, embedding piezoelectric patches. It is shown that the effects of in-plane and out-of-plane external forces can be considered as pre-stress components. These ones, at the root of buckling phenomena, alter the stiffness of the structure and shift the plate resonance frequencies. Then, by solving the eigenvalue problem of the pre-stress vibrating structure, we can find the relationship between the natural frequencies of the structure and the externally applied multi-axis force. The proof of concept of this sensor is achieved on a case study. Finally, numerical results from both, home-made and commercial, finite element software demonstrates the interest of our approach to design integrated and inexpensive multi-axis force sensors solutions

Irreversible thermodynamics and smart materials systems modelling. Example of magnetic shape memory actuators.

International audienceSmart systems is a very promising technology to design high performance and highly integrated mechatronic devices. Nevertheless, one of the main drawbacks of these devices is the complex non-linear and irreversible behaviour of the active materials at the heart of such systems. To solve these difficulties, this paper presents a thermodynamics based procedure to model more accurately active materials. After a review on energy conversion modeling techniques, the paper extends classical thermodynamics procedure to the case of irreversible processes. The use of internal state variables helps to improve the physical understanding of non-linear and irreversible mechanisms in smart materials. This procedure is applied to Magnetic Shape Memory Alloys actuators and the results are quite encouraging. Modelling methods proposed in this paper improves the understanding of complex active materials for smart systems

Magnetic manipulation with several mobile coils towards gastrointestinal capsular endoscopy.

Traditional techniques of endoscopy based on flexible endoscopes are fairly reliable but poorly tolerated by patients and do not give access to the small bowel. It has been demonstrated that magnetic fields are usable for manipulating an untethered magnet, either using fixed coils or mobile permanent magnets.We introduce a novel approach for magnetic manipulation and present the preliminary results obtained by simulating a planar manipulation system including multiple mobile coils

Fully Dynamic k -Center Clustering

International audienceStatic and dynamic clustering algorithms are a fundamental tool in any machine learning library. Most of the efforts in developing dynamic machine learning and data mining algorithms have been focusing on the sliding window model (where at any given point in time only the most recent data items are retained) or more simplistic models. However, in many real-world applications one might need to deal with arbitrary deletions and insertions. For example, one might need to remove data items that are not necessarily the oldest ones, because they have been flagged as containing inappropriate content or due to privacy concerns. Clustering trajectory data might also require to deal with more general update operations. We develop a (2 +)-approximation algorithm for the k-center clustering problem with "small" amortized cost under the fully dynamic adversarial model. In such a model, points can be added or removed arbitrarily, provided that the adversary does not have access to the random choices of our algorithm. The amortized cost of our algorithm is poly-logarithmic when the ratio between the maximum and minimum distance between any two points in input is bounded by a polynomial, while k and are constant. Our theoretical results are complemented with an extensive experimental evaluation on dynamic data from Twitter, Flickr, as well as trajectory data, demonstrating the effectiveness of our approach

Geometric analysis of the singularities of a magnetic manipulation system with several mobile coils.

International audienceIt has been demonstrated that magnetic fields are relevant for manipulating an untethered magnet, either using fixed coils or mobile permanent magnets. This paper shows however, that any magnetic manipulation method is prone to singular configurations and that the simple numerical analysis of the rank of the "manipulation matrix" is not enough to detect them. Alternatively, we propose a geometrical analysis to interpret and detect the singularities as well as to decide on the acceptability of a reference trajectory. Then, we present results obtained by simulating a planar manipulation system including a multiple mobile coils and a Helmholtz like set-up