70 research outputs found

    A solution to the stick slip problem for an electropneumatic drive

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    International audienceThis paper describes a solution to the problem of "stick-slip" for an electro-pneumatic system. The phenomenon of "stick-slip" may appear during the mechanical static state when the position is fixed but the pressures continue to evolve in each actuator chamber, until exceeding the dry friction zone. The system is then in partial equilibrium. The idea to avoid this phenomenon is a switching control law between the tracking position control and the pressure regulation

    A robust multivariable control for an electropneumatic system using backstepping design

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    International audienceDuring the last twenty years, the parallel development of pneumatic systems and control theory has lead to the implementation of modern control laws in pneumatic devices. This paper deals with the robust control problem of a pneumatic actuator subjected to mass flow leakage inside the servodistributor and load disturbances. The control strategy is based on backstepping design. For this, backstepping is presented in an informal setting. The nonlinear model of the electropneumatic system is presented. This one is transformed to be nonlinear affine model and a coordinate transformation is then related to make possible the implementation of the nonlinear controller. Control laws are developed using backstepping design to control position and pressure. The robustness visa -vis modeling errors and some unknown terms is proved. Finally, the experiment results are presented and discussed

    Direct Switching Position Control Algorithms For Pneumatic Actuators Using On/Off Solenoid Valves

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    Pneumatic actuators are advantageous in terms of cost, power to weight ratio and inherent safety. However, their dynamics makes precise closed-loop position control very difficult in practice. Two sliding-mode control algorithms for controlling the position of a pneumatic cylinder by directly switching four on/off solenoid valves are proposed in this paper. The solenoid valves are much less expensive than the commonly used servo or proportional valves. The proposed algorithms are compared to two state of the art position control algorithms. Based on experiments on a high friction cylinder with various payloads, the proposed controllers provide superior performance in terms of valve switches per second, steady state error, settling time and overshoot. The achieved number of valve switches per second is also about one tenth of the number required by the pulse-width modulation method that is commonly used with on/off valves. This should result in prolonged valve lifetimes and reduced maintenance costs

    Modeling and control of a pneumatic muscle actuator

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    This thesis presents the theoretical and experimental study of pneumatic servo position control systems based on pneumatic muscle actuators (PMAs). Pneumatic muscle is a novel type of actuator which has been developed to address the control and compliance issues of conventional cylindrical actuators. Compared to industrial pneumatic cylinders, muscle actuators have many ideal properties for robotic applications providing an interesting alternative for many advanced applications. However, the disadvantage is that muscle actuators are highly nonlinear making accurate control a real challenge. Traditionally, servo-pneumatic systems use relatively expensive servo or proportional valve for controlling the mass flow rate of the actuator. This has inspired the research of using on/off valves instead of servo valves providing a low-cost option for servo-pneumatic systems. A pulse width modulation (PWM) technique, where the mass flow is provided in discrete packets of air, enables the use of similar control approaches as with servo valves. Although, the on/off valve based servo-pneumatics has shown its potential, it still lacks of analytical methods for control design and system analysis. In addition, the literature still lacks of studies where the performance characteristics of on/off valve controlled pneumatic systems are clearly compared with servo valve approaches. The focus of this thesis has been on modeling and control of the pneumatic muscle actuator with PWM on/off valves. First, the modeling of pneumatic muscle actuator system controlled by a single on/off valve is presented. The majority of the effort focused on the modeling of muscle actuator nonlinear force characteristics and valve mass flow rate modeling. A novel force model was developed and valve flow model for both simulation and control design were identified and presented. The derived system models (linear and nonlinear), were used for both control design and utilized also in simulation based system analysis. Due to highly nonlinear characteristics and uncertainties of the system, a sliding mode control (SMC) was chosen for a control law. SMC strategy has been proven to be an efficient and robust control strategy for highly nonlinear pneumatic actuator applications. Different variations of sliding mode control, SMC with linear model (SMCL) and nonlinear model (SMCNL) as well as SMC with integral sliding surface (SMCI) were compared with a traditional proportional plus velocity plus acceleration control with feed-forward (PVA+FF) compensation. Also, the effects of PWM frequency on the system performance were studied. Different valve configurations, single 3/2, dual 2/2, and servo valve, for controlling a single muscle actuator system were studied. System models for each case were formulated in a manner to have a direct comparison of the configuration and enabling the use of same sliding mode control design. The analysis of performance included the sinusoidal tracking precision and robustness to parameter variations and external disturbances. In a similar manner, a comparison of muscle actuators in an opposing pair configuration controlled by four 2/2 valves and servo valve was executed. Finally, a comparison of a position servo realized with pneumatic muscle actuators to the one realized with traditional cylinder was presented. In these cases, servo valve with SMC and SMCI were used to control the systems. The analysis of performance included steady-state error in point-to-point positioning, the RMSE of sinusoidal tracking precision, and robustness to parameter variations

    Modeling and control of a pneumatic muscle actuator

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    This thesis presents the theoretical and experimental study of pneumatic servo position control systems based on pneumatic muscle actuators (PMAs). Pneumatic muscle is a novel type of actuator which has been developed to address the control and compliance issues of conventional cylindrical actuators. Compared to industrial pneumatic cylinders, muscle actuators have many ideal properties for robotic applications providing an interesting alternative for many advanced applications. However, the disadvantage is that muscle actuators are highly nonlinear making accurate control a real challenge. Traditionally, servo-pneumatic systems use relatively expensive servo or proportional valve for controlling the mass flow rate of the actuator. This has inspired the research of using on/off valves instead of servo valves providing a low-cost option for servo-pneumatic systems. A pulse width modulation (PWM) technique, where the mass flow is provided in discrete packets of air, enables the use of similar control approaches as with servo valves. Although, the on/off valve based servo-pneumatics has shown its potential, it still lacks of analytical methods for control design and system analysis. In addition, the literature still lacks of studies where the performance characteristics of on/off valve controlled pneumatic systems are clearly compared with servo valve approaches. The focus of this thesis has been on modeling and control of the pneumatic muscle actuator with PWM on/off valves. First, the modeling of pneumatic muscle actuator system controlled by a single on/off valve is presented. The majority of the effort focused on the modeling of muscle actuator nonlinear force characteristics and valve mass flow rate modeling. A novel force model was developed and valve flow model for both simulation and control design were identified and presented. The derived system models (linear and nonlinear), were used for both control design and utilized also in simulation based system analysis. Due to highly nonlinear characteristics and uncertainties of the system, a sliding mode control (SMC) was chosen for a control law. SMC strategy has been proven to be an efficient and robust control strategy for highly nonlinear pneumatic actuator applications. Different variations of sliding mode control, SMC with linear model (SMCL) and nonlinear model (SMCNL) as well as SMC with integral sliding surface (SMCI) were compared with a traditional proportional plus velocity plus acceleration control with feed-forward (PVA+FF) compensation. Also, the effects of PWM frequency on the system performance were studied. Different valve configurations, single 3/2, dual 2/2, and servo valve, for controlling a single muscle actuator system were studied. System models for each case were formulated in a manner to have a direct comparison of the configuration and enabling the use of same sliding mode control design. The analysis of performance included the sinusoidal tracking precision and robustness to parameter variations and external disturbances. In a similar manner, a comparison of muscle actuators in an opposing pair configuration controlled by four 2/2 valves and servo valve was executed. Finally, a comparison of a position servo realized with pneumatic muscle actuators to the one realized with traditional cylinder was presented. In these cases, servo valve with SMC and SMCI were used to control the systems. The analysis of performance included steady-state error in point-to-point positioning, the RMSE of sinusoidal tracking precision, and robustness to parameter variations

    Robust output feedback sampling control based on second order sliding mode

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    International audienceThis paper proposes a new second order sliding mode output feedback controller. This latter is developped in the case of finite sampling frequency and is using only output information in order to ensure desired trajectory tracking with high accuracy in a finite time in spite of uncertainties and perturbations. This new strategy is evaluated in simulations on an academic example

    Analyse et implémentation du contrôle par modes glissants en temps discret

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    This work is dedicated to the discrete-time version of Sliding Mode Control, a well-known technique in the field of Automatic Control.The main contribution of this research effort is the use of an implicit discretization instead of an explicit one.The main contributions in the three domains of Automatic Control are as follows: analysis of the implicitly discretized sliding mode controllers (many properties of the continuous-time version are preserved, or have very similar counterparts). Simulations were run using a new Control toolbox in Siconos, a platform dedicated to the simulation of non-smmooth dynamical system. Finally, experiments confirm the superiority of the implicit discrete-time sliding mode controllers.Cette thèse concerne la commande par modes glissants en temps discret. L'axe principal de ce travail fut l'utilisation d'une méthode de discrétisation implicite et non explicite pour la partir discontinue de la commande. Les contributions majeures sont : l'analyse de la commande par mode glissant discrétisée implicitement (stabilité, rejet de perturbations, ...). Des simulations, réalisées à l'aide d'un nouveau module "Control" dans la plateforme Siconos, illustrent certains résultats théoriques. Enfin des essais expérimentaux confirment la supériorité de la discrétisation implicite sur celle de l'explicite
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