This paper proposes a cascade controller with friction compensation based on the LuGre model. This control is applied to a pneumatic positioning system. The cascade methodology consists of dividing the pneumatic positioning system model into two subsystems: a mechanical subsystem and a pneumatic subsystem. This division allows the introduction of friction compensation at force level in the pneumatic positioning system. Using Lyapunov's direct method, the convergence of the tracking errors is shown under the assumption that the system parameters are known. Experimental results illustrate the main characteristics of the proposed controller

This paper addresses a new methodology for servo pneumatic actuators mathematical modeling and selection from the dynamic behavior study in engineering applications. The pneumatic actuator is very common in industrial application because it has the following advantages: its maintenance is easy and simple, with relatively low cost, self-cooling properties, good power density (power/dimension rate), fast acting with high accelerations, and installation flexibility. The proposed fifth-order nonlinear mathematical model represents the main characteristics of this nonlinear dynamic system, as servo valve dead zone, air flow-pressure relationship through valve orifice, air compressibility, and friction effects between contact surfaces in actuator seals. Simulation results show the dynamic performance for different pneumatic cylinders in order to see which features contribute to a better behavior of the system. The knowledge of this behavior allows an appropriate choice of pneumatic actuator, mainly contributing to the success of their precise control in several applications.

This work presents a new methodology for dead zone nonlinearity identification in proportional directional pneumatic valves. It is based on observing the dynamic behaviour of the pressure in the valve gaps. Dead zone is common in hydraulic and pneumatic valves because the spool blocks valve orifices with some overlap, so that for a range of spool positions there is no fluid flow. The dead zone nonlinearity is a key factor that limits both static and dynamic performance in feedback control of fluid power systems. The usual method to cancel the harmful effects of dead zone is to add its fixed inverse function into the controller. This inverse is modelled by a set of parameters that need to be identified. The classic dead zone parameter identification uses expensive flow transducers and special test rig, while our proposed methodology needs only pressure transducers. Experimental results illustrate the efficacy of this methodology that is cheaper and faster.

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High wheat yields, besides the genetic potential and edaphoclimatic conditions, are obtained by proper management and nitrogen use. The objective of the study was to define the most appropriate time for N-fertilizer application, considering the range of greatest wheat requirements, dependent on the succession system type and the predictability of favorable and unfavorable years. The study was carried out in the 2008 to 2012 years, in Augusto Pestana, Rio Grande do Sul, Brazil. The experimental design was randomized blocks with four replications, with N-fertilizer application at 0, 10, 30 and 60 days after emergence, considering the corn/wheat and soybean/wheat succession system. The study found that the best time for nitrogen fertilizer application on wheat is mostly influenced by the year of cultivation and is less influenced by the succession system type. The appropriate time for the Nfertilizer application in favorable years of cultivation was about 45 days after emergence. In unfavorable years, it must be anticipated. Regardless of the cultivation year and the succession system type, the Nfertilization at 30 days after emergence evidenced the highest means as the most stabile grain yield.