Limited energy consumption in positioning control of an electropneumatic actuator

International audienceThis paper shows the possibility of using two three-way servo-distributors in place of one five-way for position control of an electropneumatic actuator. Two nonlinear control laws are developed and compared. The aim is to prove the advantage of a multi-input control law in terms of stability and energy consumption due to the flatness property

A Biomimetic steering robot for Minimally invasive surgery application

International audienceMinimally Invasive Surgery represents the future of many types of medical inter- ventions such as keyhole neurosurgey or transluminal endoscopic surgery. These procedures involve insertion of surgical instruments such as needles and endoscopes into human body through small incision/ body cavity for biopsy and drug delivery. However, nearly all surgical instruments for these procedures are inserted manually and there is a long learning curve for surgeons to use them properly. Many research efforts have been made to design active instruments (endoscope, needles) to improve this procedure during last decades. New robot mechanisms have been designed and used to improve the dexterity of current endoscope. Usually these robots are flexible and can pass the constrained space for fine manipulations. In recent years, a con- tinuum robotic mechanism has been investigated and designed for medical surgery. Those robots are characterized by the fact that their mechanical components do not have rigid links and discrete joints in contrast with traditional robot manipula- tors. The design of these robots is inspired by movements of natural animals such as tongues, elephant trunks and tentacles. The unusual compliance and redundant degrees of freedom of these robots provide strong potential to achieve delicate tasks successfully even in cluttered and unstructured environments. This chapter will present a complete application of a continuum robot for Mini- mally Invasive Surgery of colonoscopy. This system is composed of a micro-robotic tip, a set of position sensors and a real-time control system for guiding the explo- ration of colon. Details will be described on the modeling of the used pneumatic actuators, the design of the mechanical component, the kinematic model analysis and the control strategy for automatically guiding the progression of the device inside the human colon. Experimental results will be presented to check the perfor- mances of the whole system within a transparent tube

A comparative study between two control laws of an electropneumatic actuator

International audienceThis paper focuses on a comparison between two positioning control laws of a half meter stroke electropneumatic disymmetrical cylinder controlled by two three-way servo-distributors : a fixed gains control law and a control law with scheduling gains. Using physical laws, the first part of this paper describes a nonlinear model of this process and focuses on the difficulty for obtaining servo-distributors mass flow rates. A specific choice of the control inputs leads to a single input model. A tangent linearised model is obtained. The two different control laws are described and implemented using a well-known dSPACE interface card. Experimental results obtained for point to point control are presented and discussed

Fluid mechanical response of a pulse tube cryocooler: modelling and experimental validation

International audienceEarth observation satellites require cryocoolers to cool down their infrared imagers at very low temperatures. Besides having very good thermodynamic performances, satellite cryocoolers are expected to generate as little vibrations as possible. In order to better understand vibration causes between 50 and 500 Hz, a precise model of the whole cryocooler is necessary. In the literature, two main modelling approaches for pulse tube cryocoolers exist: compressor-oriented models reduce the thermodynamic system to a linear mass-spring-damper system acting on compressor's pistons; and thermodynamically oriented models aimed at understanding and predicting thermodynamic performances. In this paper, the mechanical behavior of the thermodynamic system is modelled. Assumptions concerning gas properties and thermodynamic behavior are made based on SAGE software simulations. A simplified Redlich Kwong equation is used. When necessary, polytropic coefficients were identified using simulation data, as were the time-averaged temperatures. The thermodynamic system is split into volumes, pipes and regenerators: conservation laws in volumes are integrated, dynamic mass and momentum conservation equations in pipes are solved using the method of characteristics and equations in regenerators are solved using a finite difference method. Three friction laws are used: one for straight pipes (Moody chart), another for wound pipes (White's correlation) and a last one for porous media (Modified Ergun equation). Porosity is measured by weighing. The model is built to respect integral causality and propagation phenomena. The developed model is validated using experimental data. The simulations highlight the non-linear mechanical behavior of the thermodynamic system: a sinusoidal motion of the pistons induces a non-sinusoidal pressure in the compression chamber. Among other, first and second harmonics amplitudes are about 3% of fundamental pressure amplitude. This model can now be integrated into a global cryocooler model to predict compressor's vibrations, power consumption or electrical harmonics. It could also be extended to predict vibrations from the thermodynamic system