Prestiction friction compensation in direct-drive mechatronics systems

LuGre model has been widely used in friction modeling and compensation.However,the new friction regime,named prestiction regime,cannot be accurately characterized by LuGre model in the latest research.With the extensive experimental observations of friction behaviors in the prestiction,some variables were abstracted to depict the rules in the prestiction regime.Based upon the knowledge of friction modeling,a novel friction model including the presliding regime,the gross sliding regime and the prestiction regime was then presented to overcome the shortcomings of the LuGre model.The reason that LuGre model cannot estimate the prestiction friction was analyzed in theory.Feasibility analysis of the proposed model in modeling the prestiction friction was also addressed.A parameter identification method for the proposed model based on multilevel coordinate search algorithm was presented.The proposed friction compensation strategy was composed of a nonlinear friction observer and a feedforward mechanism.The friction observer was designed to estimate the friction force in the presliding and the gross sliding regimes.And the friction force was estimated based on the model in the prestiction regime.The comparative trajectory tracking experiments were conducted on a simulator of inertially stabilization platforms among three control schemes:the single proportional–derivative(PD)control,the PD with LuGre model-based compensation and the PD with compensator based on the presented model.The experimental results reveal that the control scheme based on the proposed model has the best tracking performance.It reduces the peak-to-peak value(PPV)of tracking error to 0.2 mrad,which is improved almost 50%compared with the PD with LuGre model-based compensation.Compared to the single PD control,it reduces the PPV of error by 66.7%.

Parameter identification of inertially stabilized platforms using current command design

Accurate parameter identification is essential when designing controllers for inertially stabilized platforms （lSPs）. But traditional identification methods suffer from observation measurement noise and operating restrictions of ISPs. To address this issue, a novel identification method based on current command design and multilevel coordinate search （MCS） algorithm without any higher order measurement differentiations was proposed. The designed current commands were adopted to obtain parameter decoupled models with the platform operating under allowable conditions. MCS algorithm was employed to estimate the parameters based on parameter decoupled models. A comparison experiment between the proposed method and non-linear least square method was carried out and most of the relative errors of identified parameters obtained by the proposed method were below 10%. Simulation and experiment based on identified parameters were conducted. A velocity control structure was also developed with disturbance observer （DOB） for application in disturbance compensation control system of an ISR Experimental results show that the control scheme based on the identified parameters with DOB has the best disturbance rejection performance. It reduces the peak to peak value （PPV） of velocity error integral to 0.8 mrad which is much smaller than the value （10 mrad） obtained by the single velocity controller without DOB. Compared with the control scheme based on sweep model with DOB compensation, the proposed control scheme improves the PPV of velocity error integral by 1.625 times.

Soil conservation and sustainable development goals(SDGs)achievement in Europe and central Asia:Which role for the European soil partnership?

Voluntary soil protection measures are not sufficient to achieve sustainable soil management at a global scale.Additionally,binding soil protection legislation at national and international levels has also proved to be insufficient for the effective protection of this almost non-renewable natural resource.The European Soil Partnership(ESP)and its sub-regional partnerships(Eurasian Sub-Regional Soil Partnership,Alpine Soil Partnership)were established in the context of FAO's Global Soil Partnership(GSP)with the mission to facilitate and contribute to the exchange of knowledge and technologies related to soils,to develop dialogue and to raise awareness for the need to establish a binding global agreement for sustainable soil management The ESP has taken a role of an umbrella network covering countries in Europe and Central Asia.It aims to improve the dialogue in the whole region and has encouraged establishing goals that would promote sustainable soil management taking into account various national and local approaches and priorities,as well as cultural specificities.The ESP first regional implementation plan for the 2017—2020 period was adopted and implemented along the five GSP pillars of action.Building on the experience of the last four years,this study demonstrates that establishing sub-regional and national partnerships is an additional step in a concrete sustainable soil management implementation process.It also suggests that a complementary approach between legal instruments and voluntary initiatives linked to the development of efficient communication and strong commitment is the key to success.