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Two main challenges in using a pneumatic artificial muscle (PAM) actuator are the nonlinearity of pneumatic system and the nonlinearity of the PAM dynamics. The latter is complicated to characterize. In this paper, a Maxwell-slip model used as a lumped-parametric quasi-static model is proposed to capture the force/length hysteresis of a PAM. The intuitive selection of elements in this model interprets the unclear, but blended contributing causes of the hysteresis very well, which are assumed to originate from the dry friction of the double helix weaving of the PAM braided shell, the friction of the weaving and the bladder, the elasticity of the bladder and/or the deformation of the conical parts of a PAM close to the end caps. The obtained model is simple, but physically meaningful and easy to handle in terms of control. [ABSTRACT FROM PUBLISHER]

Draft force prediction and soil mechanical behavior during soil de-compaction was implemented by using the Discrete Element Method. The model parameters were defined as a function of the mechanical properties a clay soil, previously obtained by laboratory tests. The properties used by the model are cohesion, adhesion, internal friction, external friction, Young's modulus and Poisson's coefficient. The effect of the subsoiler shape variation was simulated under dry-compacted soil conditions, showing clear variations in forces related with the tool geometry. Increasing in complexity of the tool geometry the simulation, the model showed advantages in terms of demanded pressure and volume of soil disrupted. The soil de-compaction with hardpan formation was also simulated by introducing two different compacted soil sections in the virtual block. The compaction level was defined by two set of micro-particles with different density resulting from modifying the soil dry bulk density at the model macro-parameter. The simulation shows the feasibility of modelling separately the forces demanded for the different part of the tillage tool and the soil particle pattern of movement during the operation. [ABSTRACT FROM AUTHOR]

In the present study the discrete element method is used for predicting forces reactions and soil behavior during non-inversion tillage. The numerical model at particle level works with a force system integrated by normal, shear, cohesion and friction forces. Macro parameters are defined as the soil mechanical properties obtained by soil mechanical tests. The behavior of soil-soil and soil-metal interface at different dry bulk densities and gravimetric water contents were determined by modified direct shear box and triaxial compression tests. A set of statistical regression equations feasible to estimate the macro values of Young's modulus, shear strength, soil friction and soil cohesion were obtained. The relationship between macro and micro behavior of soil friction was investigated by means of the simulation of direct shear tests. The discrete soil model was used to simulate soil tillage at conditions called hard-dry, soft-wet and friable state. To calibrate the model, a soil-bin was filled with the soil previously characterized and equipped with a tool similar to the one used for the simulation. A National Instrument Data Logger system was configured aimed at measuring vertical and horizontal reaction forces. The comparison between draft forces from simulation and soil-bin tests showed a small under-predicted behavior of the model for loose soil with high moisture; this behavior was fixed toward compacted and dry soil conditions. Para-plough and moldboard were the tools used for non-inversion tillage simulation at different physical states of the soil. The result shows the pattern of movement and force distribution related with the geometry of the tool. [ABSTRACT FROM AUTHOR]

Friction and cohesion in efforts that take place during soil deformation calculations. For interactions are considered normal force, tangential cohesive friction. The maximum shear is governed by the criterion of Mohr-Coulomb failure. Model calibration is performed by obtaining the relationship between micro and macroscopic parameters used in the model. The calibration of the friction was carried out by simulating the direct shear test of a sample of soil micro different friction coefficients. To calibrate cohesion used different values of cohesion at the micro and the relationship was obtained by modifying the micro friction values by simulating the biaxial compression test. The friction results showed a linear relationship regarding the variation of the micro value. Instead cohesion was linearly affected by the change in the quadratic micro-cohesion and friction over micro. [ABSTRACT FROM AUTHOR]