Two typical characteristics of direct piezoelectric actuators are displacements of ten micrometers and high stiffnesses. recently, multilayers actuators have been improved, and they now display strains of approximately 1200ppm at low excitation levels (less than two hundred volts). Thus, they are well suited to perform precise positioning of optical devices. But for industrial needs, this performances is still insufficient for positioning devices with larger displacements (in the range of several hundred micrometers).
The MRF actuators are new electromechanical components using Magneto Rheological Fluids (MRF). These smart fluids are characterized by their ability to change their rheological properties versus applied magnetic field. They can switch from a liquid to an almost solid body. This effect is reversible and operates within a few milliseconds. MRF are used to create controllable dampers, smart shock absorbers or brakes. After having developed several MRF actuators with an original characteristic (presenting a blocking force at rest), Cedrat Technologies was asked to develop a very challenging new MRF damper which goal can be summed up with a few words: “small size and high force”.
Optical instruments such as interferometers and optical delay lines are sensitive to external vibrations and require a strong isolation of vibrations. Some products for active, semi active or passive isolation exist but are rather large which makes them much more suitable for lab applications than to embedded applications as meet in Space, Aircraft or Military applications in general, or in the space ICE CNES experiment. These requirements have driven the development of a new type of Electrically-Tunable Low-Frequency Miniature Suspension.
Actuation is used in all vehicles (aircraft, spacecraft, ground vehicles, etc) to control the position and/or attitude of the vehicle, and also to deploy or retract equipment, particularly for embedded optic instruments (cameras, telescopes). As such, the actuation is a safety critical system, particularly when humans could be catastrophically affected by failures within the system. Applications for actuation are flight controls, landing gear, rotors, suspension, antennae steering, valves, scanning, positioning using hydraulic, electromechanical, magnetic and piezo actuators. In aircraft there is a common goal to reduce the number of hydraulic actuators in vehicles and eventually to replace them completely by electric actuators.
Stepping Piezo Actuators (SPA) are long stroke linear piezoelectric actuators capable to reach long stroke (typ. >10mm) with an important resolution (typ. <1nm). It has been proposed to use Amplified Piezo Actuator into inertial stepper motor to build the SPA. This piezo motor showed good behaviour, with relatively high speed (up to 70mm/s), force (from 0.2N to 20N) and low consumption (down to 700mW).
Off-pump Coronary Artery Bypass Grafting (CABG) is still today a technically difficult procedure. In fact, the mechanical stabilizers used to locally suppress the heart excursion have been demonstrated to exhibit significant residual motion. We therefore propose a novel active stabilizer which is able to compensate for this residual motion. The interaction between the heart and a mechanical stabilizer is first assessed in vivo on an animal model. Then, the principle of active stabilization, based on the high speed vision-based control of a compliant mechanism, is presented. In vivo experimental results are given using a prototype which structure is compatible with a minimally invasive approach.
MRF actuators are new electromechanical components using Magneto Rheological Fluids (MRF). When submitted to a high enough magnetics fiels, MRF switch from a liquid to a near solid body.
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