Quad-rotor is very suitable for payload transportation due to the merits of high maneuverability and free hovering. However, the unknown varying payloads can cause negative influences that act in forms of persistent disturbances and sudden changes, damaging flight performance especially the attitude stability seriously. Targeting the persistent disturbances, an entirely novel disturbance estimator (DE) which can estimate non-smooth disturbances in a highly accurate manner for feedback compensation is proposed in this paper. To deal with the sudden changes from prescribed references and the payloads that may induce too large overshoots and input surging, a type of predictive optimal controller, which considers tracking errors and their changing rates of a class of linear multiple-input-multiple-output systems, is developed. Simulation results show that the system enhanced by the DE has better control performance than the ones enhanced by the commonly used extended state observer or nonlinear disturbance observer. Compared with the typical control approaches, the proposed control scheme enables the quad-rotor attitude system more stable performance and more ideal inputs on both persistent disturbance and sudden change resisting during payload transportation. INDEX TERMS Quad-rotor, payload transportation, disturbance attenuation, predictive optimal control.
This study investigated the influences of Cu, high temperature-treated Cu (H-Cu) and graphene-coated Cu (G-Cu) substrates on interfacial reaction, microstructure and hardness of Sn-3.0g-0.5Cu (SAC305) solder alloy. Intermetallic compound (IMC) layer evolution and mechanical property of Sn-3.0g-0.5Cu-0.3Ni (SAC305-0.3Ni) solder joints were also studied under different aging duration. A continuous scallop-like IMC layer was observed at SAC305/Cu, SAC305/H-Cu, SAC305/G-Cu interfaces during reflow and isothermal aging. After adding Ni in the SAC305-0.3Ni solder alloy, the roughness of IMC layer on Cu, H-Cu substrates increased. In contrast, the addition of Ni had a limited impact on the roughness of IMC layer on G-Cu substrates. The total thickness of IMC layer grew as aging time increases, proportionated to the square root of aging duration. The addition of Ni in the solder alloy promoted the growth of IMC layer on Cu and H-Cu substrates, but it was restrained on G-Cu substrate. The amount of the IMC phases in SAC305 and SAC305-0.3Ni solder bulks on the three substrates increased significantly as aging time prolonged. Thus, the hardness of SAC305 and SAC305-0.3Ni solder bulks on the three substrates rose. The addition of Ni in the solder bulks on the three substrates sharply enhanced the formation of [Formula: see text]-Sn phases and increased the quantity of the IMCs. Consequently, the hardness of SAC305-0.3Ni solder bulks was higher than that of SAC305 solder bulk on the three substrates under same aging condition. In addition, the graphene-coated layer on G-Cu substrate could improve the hardness of SAC305 and SAC305-0.3Ni solder bulks.
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