Integrative Tracking Control Strategy for Robotic Excavation

Automated excavation is hard to achieve due to several inherent problems such as resistive force acting against the bucket, non-homogenous dynamics of various excavation media, and nonlinearities of the excavator’s hydraulics system. To deal with this issue, this paper provides an integrative control strategy for successful autonomous excavation that considers the mutually associated factors, i.e., position, contour, and force control. For the position tracking, a non-linear PI controller was designed to track the position of individual actuators of the excavator and thereby control the bucket tip’s position. In addition, the contour control technique was applied to achieve an optimal excavation path to minimize contour errors. Finally, to compensate for the ground resistive force during digging tasks, a force impedance controller was designed along with the time-delayed control that reduces the effect of dynamic uncertainties. Experimental results with a modified mini-wheeled excavator show that the developed integrative tracking control strategy can provide a comprehensive solution to improving the tracking performance for autonomous excavation that can simultaneously deal with the critical components of position, contour, and force control.

     

Effect of Cu and Li Contents on the Serrated Flow Behavior of Al-Cu-Li Based Alloys

Metallurgical and Materials Transactions A - The serrated flow behavior of Al-Li, Al-Cu and Al-Cu-Li alloys was studied in solution-treated condition under a range of strain rates at ambient...     

Evolution of hierarchically formed petal-like 3 dimensional layer structures for SnS2 via ratio control of Sn/thiourea and their electrochemical charge storage behavior

Herein, the successful synthesis of tin sulfide compounds by a facile one-step solvothermal method is reported, and its evolution of hierarchically formed petal-like 3-dimensional layer structures for SnS₂ via ratio control of Sn/thiourea(TU) is systematically investigated. With the increase of TU content, the two-dimensional layered structure is clearly changed from discrete to hierarchically dense nanostructure. Thus, among various conditions, SnS₂ with 1:2 ratio (SNS12) shows superior electrochemical performance associated with its discrete nanostructure. In this study, sample SNS12 shows a high specific capacitance of 1403 F g^-1 at 1 mVs^-1, a high power density of 456.42 W h kg^-1 at an energy density of 46.84 W kg^-1 with the stable cyclic performance of 85.87% up to 5000 cycles. The enhanced electrochemical performances are attributed to its unique ultrathin petal discrete structure, which allows for fast ion/electron transfer, high active sites, short diffusion distance, and more electrolyte/electrode interface access. Moreover, a fabricated symmetric supercapacitor device has a high capacity to operate commercial LED, leading to the validation of its practical operation durability for synthesized material on a device-level application. This study suggests that favorably layered 3D SnS₂ electrode materials and their controllable protocols via Sn/TU ratio modulation could be one of the beneficial direction for the envisioned energy storage applications.     

Sub-zero Temperature Dependence of Tensile Response of Friction Stir Welded Al-Cu-Li (AA2198) Alloy

Mechanical properties at ambient and cryogenic temperatures of Al-Cu-Li alloy are required for design and fabrication of liquid hydrogen and liquid oxygen tanks of satellite launch vehicles. In the present work, bead-on-sheet, friction stir welding was carried out with three different rotation speeds. The yield and strain hardening behaviors of the welds were evaluated in temperature range of 20 K to 298 K. Both yield stress and strain hardening ability in the specimen increased with decrease in testing temperature. The dependence of yield stress on temperature was modeled on the basis of thermally activated dislocation mobility, while that of strain hardening was modeled on the temperature dependence of dynamic recovery rate parameter. The recovery parameter followed an Arrhenius-type relationship with temperature. The model parameters determined from the experimental data were further used to simulate the stress–strain curves at different sub-zero temperatures for the friction stir welds.

     

Designing of fuzzy expert heuristic models with cost management toward coordinating AHP,fuzzy TOPSIS and FIS approaches

In genuine industrial case, problems are inescapable and pose enormous challenges to incorporate accurate sustainability factors into supplier selection. In this present study, three different primarily based multi-criteria decision making fuzzy models have been compared with their deterministic version so as to resolve fuzzy prioritization problems. The developed model applies AHP, TOPSIS and fuzzy inference system (FIS) using a MATLAB toolbox to effectively analyze the interdependencies between sustainability criteria and select the best sustainable supplier in the fuzzy environment, while capturing all objective criteria. A typical supplier A4 has been awarded the most suitable supplier with 0.386 composite relative weights of AHP, relative closeness to ideal solution 0.7154 and normalized score index 0.219 FIS model using MATLAB toolbox.     

Deformation behaviour of Al–Cu–Li alloy containing T1 precipitates

In the present work, a systematic investigation of crystallographic texture evolution and strain hardening behaviour was undertaken to comprehend the deformation behaviour in the presence of T₁ (Al₂CuLi) precipitates. Characteristic texture components symbolising multiple slip condition such as Copper and S were observed upon rolling which is in contrast with other Al alloys containing shearable precipitates. Strain hardening ability was also observed to be remarkably high in the presence of T₁ precipitates. The texture and strain hardening results are compared with another age hardenable Al alloy (Al–Mg–Si alloy) containing shearable precipitates to clearly bring out the difference in the nature of T₁ precipitates.