Sylvie Sesmat

Control of an electropneumatic actuator: comparison between some linear and non-linear control laws

Abstract The aim of this paper is to present and to compare some linear and non-linear control laws for an electropneumatic positioning system both for point-to-point control and for tracking control. The experimental results are presented in terms of repeatability for each control law implemented on the same device: an in-line electropneumatic servo-drive. Different kinds of model, namely a non-linear affine model, linearized tangent model and a reduced linearized tangent model, are presented to synthesize the different control laws. For this a new mathematical modelling of the servo-distributor flow stage is described.

Electropneumatic Cylinder Backstepping Position Controller Design With Real-Time Closed-Loop Stiffness and Damping Tuning

This paper develops a backstepping-based algorithm to control the position of an electropneumatic actuator while allowing the precise tuning of the closed-loop stiffness and damping. The proposed strategy offers an efficient method to choose the controller parameters based on a physical and linear analysis. The strict feedback form of the model, which is required in order to apply the backstepping methodology, is obtained through the use of a transformation of the systems inputs. The proposed multiple input multiple output control law as well as its parameters tuning method are validated experimentally. The experimental results are provided using an innovative test bench combining an electropneumatic cylinder and an electric linear motor. The two main contributions are: 1) the use of a new decoupling transformation to control the systems 2 DOF and 2) the description of a closed-loop damping and stiffness tuning strategy. Simultaneous position and stiffness control result in a more precise and adjustable variable stiffness actuator than the simultaneous pneumatic force-stiffness control laws generally encountered in the literature. Moreover, a specific study is conducted to clarify the interaction between pneumatic and closed-loop stiffnesses in order to combine the advantages of passive and active compliant actuators.

HYBRID FORCE CONTROL WITH ON/OFF ELECTROPNEUMATIC STANDARD DISTRIBUTORS

Abstract This paper presents a new control method applied to the electro-pneumatic field. This strategy originates from the hybrid control theory recently developed for the control of asynchronous or synchronous electrical motors, e.g. Retif (2004). The interest of this strategy concerns the possibility of using standard on/off distributors instead of the usual servodistributors (components issued from proportional technology) for the force control of a pneumatic cylinder. Distributor components have less performance but are cheaper than a servodistributor. The aim is to obtain, with a distributor, the same performances as servodistributors on the global system. Based on both cylinder and distributor models, the hybrid control presented here chooses the best state for each on/off distributor to reach the desired force value. Experimental results are presented and discussed.

A Biomimetic steering robot for Minimally invasive surgery application

Minimally 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.

Bond Graph model of the intermediate block in a hydraulic control system

The intermediate block, as a basic element in the hydraulic control system, is used to install all hydraulic components and guides the fluid flows. The effect of this block, usually neglected, is taken into consideration in this paper since it is a part of a system developed for high performance applications and especially high frequencies [7]. By means of the Bond Graph tool, a detailed model is established. This model could then be easily integrated into the Bond Graph model of the whole system. Besides, the relationship between flow rates and pressure drops along with the energy losses in the block are obtained according to a method based on the decomposition of the circuit in parts for which the local losses can be obtained from abacuses. The computational fluid dynamics (CFD) is used for the validation of the results.

IDENTIFICATION OF PHYSICAL PARAMETERS OF A PNEUMATIC SERVOSYSTEM

Abstract This paper deals with the estimation of physical parameters of a pneumatic servo positioning system. It consists of two servodistributors and an actuator. This work concerns not only the identification of the mass, viscous and Coulomb non symmetric frictions parameters of the mechanical part but also the polytropic coefficient of the gas considered as a perfect one. At first the mass flow rate characteristic of the servodistributor is determined indirectly by an approximation using several polynomial functions. Next, a dynamic model which is linear in relation to a set of dynamic parameters is proposed. The dynamic parameters are estimated using the weighted least squares solution of an over determined linear system obtained from the sampling of the dynamic model along a closed loop tracking trajectory. An experimental study exhibits good identification results.