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.

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.

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Nitrogen fertilizer management modifies oat (Avena sativa) panicle components and its grain yield. The work aims to study the potential of the variables of oat (A. sativa) panicle with N-fertilizer, and to simulatate its grain yield using multiple linear regression in succession systems of high and reduced Nresidual release. The study was done in 2013 and 2014. The experiment was done in a complete randomized block of 4×2 factorial design, with four replications. The treatments include: nitrogen fertilizer of four doses (0, 30, 60 and 120 kg ha-1), oat (A. sativa) cultivars at two levels (Barbarasul and Brisasul) and succession system at two levels (soybean/oat (A. sativa) and corn/oat (A. sativa). The multiple linear models were efficient in the harvest index of panicle of soybean/oat (A. sativa) system, regardless of the dose evaluated. However, at high doses, the number of grain per panicle was included. In the corn/oat (Avena sativa) system, the harvest index of panicle, the number of grains and spikelets panicle were adjusted based on the model. The multiple linear regression efficiently simulates N-fertilizer to affect the grain yield of oat (Avena sativa) and one or more potential variables of panicle in the succession systems.

Fuzzy logic can simulate wheat productivity by assisting crop predictability. The objective of the study is the use of fuzzy logic to simulate wheat yield in the conditions of nitrogen use, together with the effects of air temperature and rainfall, in the main cereal succession systems in Southern Brazil. The study was conducted in the years 2014, 2015 and 2016, in Augusto Pestana, RS, Brazil. The experimental design was a randomized block design with four repetitions in a 4 x 3 factorial scheme for N-fertilizer doses (0, 30, 60, 120 kg ha-1) and nutrient supply forms [100% in phenological stage V3 (third expanded leaf); (70%/30%) in the phenological stage V3/V6 (third and sixth expanded leaf) and; fractionated (70%/30%) at the phenological stage V3/E (third expanded leaf and beginning of grain filling)], respectively, in the soybean/wheat and corn/wheat systems. The pertinence functions and the linguistic values established for the input and output variables are adequate for the use of fuzzy logic. Fuzzy logic simulates wheat grain yield efficiently in the conditions of nitrogen use with air temperature and rainfall in crop systems.

The biomass productivity and wheat grains efficiency is determined by nitrogen dose adjustment (full or fractioned), environmental conditions, and cropping system. The aim of this study was to improve the efficiency of N-fertilizer usage on wheat to maximize the biomass productivity and grain yield by adjusting the full or fractioned nitrogen dose in favorable and unfavorable year conditions, in succession systems with high and reduced N-residual release. In this study, two experiments were conducted between 2012 and 2014. One was to quantify the biomass productivity rate and another to determine grain yield. The experimental design was a complete randomized block, with four replications, in a 4 × 3 factorial scheme to N fertilizer rates (0, 30, 60 and 120 kg ha-1) and supply forms of the nutrient [full dose (100%) in the V 3 phenological stage (third expanded leaf); fractioned (70 and 30%) at the V 3 and V 6 phenological stages (third and sixth expanded leaf, respectively) and; fractionated (70 and 30%) at the V 3 and E phenological stages (third expanded leaf and early grain filling), ] respectively, in soybean/wheat and maize/wheat cultivation systems. The nitrogen supply in wheat through single dose or fraction indicates linear tendency over the productivity biomass daily rate-1 with the increase of N-fertilizer, regardless of a favorable and unfavorable year and system of a succession of the high and reduced N-residual release. However, in favorable years, the use of full dose on V 3 stage is indicated. In the maize/wheat system, the full dose at V 3 stage is more efficient, especially with higher doses of the nutrient. For grain yield, the N-fertilizer fractioning was adjusted in intermediate cropping years, while the full dose became suitable at the V 3 stage in favorable years. However, in unfavorable years, nitrogen investments should be minimized, regardless of the supply form and succession system.