Sensorless Optimal Switching Impact/Force Controller

Intelligent interaction control is required in many fields of application, in which different operative situations have to be faced with different controllers. Being able to switch between optimized controllers is, indeed, of extreme importance to maximize the task performance in the different operative conditions (i.e., free-space motion and contact), especially when considering sensorless robots. To deal with the proposed context, a sensorless optimal switching impact/force (OSIF) controller is proposed. The low-level robot control is composed of an inner joint position controller, fed by an outer Cartesian impedance controller with a reference position. The estimation of the external wrench is implemented by means of an Extended Kalman Filter (EKF). The high-level controller (feeding the Cartesian impedance controller with the setpoint) is composed of an optimized impact controller (LQR-based controller), an optimized force controller (SDRE-based controller), and a continuous switching mechanism (Fuzzy Logic-based). In addition, the output of the switching mechanism is used to adapt the Cartesian impedance control parameters (i.e., stiffness and damping parameters). Experimental tests have been performed on a Franka EMIKA panda robot to validate the proposed controller. Obtained results show the capabilities of the OSIF controller, being able to detect task phase transitions while satisfying the target performance

Effets du froid sur les stades précoces de développement du maïs (Zea mays L.) (synthèse bibliographique)

Effects of cold temperatures on the early stages of maize (Zea mays L.). A review. Introduction. Maize is a crop of great economical importance. Despite its tropical origin and its high sensitivity to low temperatures, maize is now cultivated in a wide range of latitudes. To maintain competitive yields, many genetic and agricultural adaptations have been implemented. Literature. Plant responses to environmental stresses such as drought or cold have been extensively studied. This article reviews the progress and current knowledge regarding the effects of non-freezing cold temperatures on maize plants, from germination to floral transition. During the early stages of development, cold alters plant phenology and productivity, mainly because of its negative impact on photosynthesis. Plant growth is affected and secondary osmotic and oxidative stresses induce cell damage. Conclusion. A better understanding of the effects of cold will allow the development of new strategies for improving plant tolerance through the use of various physiological, genetic and molecular approaches

External joint torques estimation for a position-controlled manipulator employing an extended kalman filter

Industrial robots are required to interact with the surrounding environment to perform a given task (e.g., an assembly task). However, standard industrial robots are commonly position-controlled. Therefore, there is the need to implement an outer compliance controller to guarantee a safe interaction. Such compliance controllers require force/torque measurements to close the loop, and most of the industrial manipulators available on the market do not have embedded force/torque sensor(s), requiring additional efforts (i.e., additional costs and implementation resources) for such integration in the robotic setup. To provide a standard industrial sensorless position-controlled robot with the capabilities to execute an interaction task, the proposed paper defines an external joint torques observer for the implementation of an outer sensorless compliance controller. More in detail, exploiting the resulting position-controlled robot dynamics, an Extended Kalman Filter (EKF) is proposed to estimate the external joint torques. Exploiting such an estimation, an outer impedance controller can be designed, providing a position/velocity reference to the inner position controller. The described approach has been validated with experiments on a Franka EMIKA panda robot. A human operator interacts with the controlled robot, applying external wrenches (i.e., both Cartesian forces and torques). The resulting external joint torques are estimated making use of the proposed EKF, comparing the achieved results with the signals provided by the joint torque sensors of the Franka EMIKA panda robot (measurements used as a baseline for validation purposes). Experimental results show the capabilities of the proposed control framework in estimating the applied external joint torques while implementing a position control-based compliance controller

EM wave propagation experiment at E band and D band for 5G wireless systems: Preliminary results

Preliminary results on an electromagnetic wave propagation experiment at E and D band are presented. The research activity is collaboration between Politecnico di Milano and the Huawei European Microwave Centre in Milan, which has recently installed short (325 m) terrestrial links operating at 73, 83, 148 and 156 GHz and connecting two buildings in the university main campus. Received power data are processed to identify and isolate rain events and quantify the fade induced by precipitation, AR. Moreover, AR is estimated taking advantage of ancillary data collected by a laser-based disdrometer collocated with the link transceivers. Preliminary results definitely point out the higher prediction accuracy achieved by exploiting the information on the rain drop size provided by the disdrometer

The Impact of Rain on Short {E} -Band Radio Links for 5G Mobile Systems: Experimental Results and Prediction Models

The results from 1 year of data collected during an electromagnetic wave propagation experiment at {E} -band are presented. The research activity originates from the collaboration between Politecnico di Milano, Milan, Italy, and the Huawei European Microwave Centre in Milan, which installed short (325 m) terrestrial links operating at 73 and 83 GHz, connecting two buildings in the university main campus. The received power data are processed, using a novel approach, to identify rain events and to remove the wet antenna effect, with the aim of accurately quantifying the fade induced by precipitation, A_{R}. Moreover, A_{R} is estimated by taking advantage of the ancillary data collected by the laser-based disdrometer collocated with the link transceivers. The results definitely point out the higher prediction accuracy achieved by exploiting the information on the rain drop size. A full year of data are used as reference to test the accuracy of the statistical prediction model for terrestrial links currently recommended by the ITU-R, which reveals a large overestimation. Finally, alternative models providing a higher accuracy are proposed and their accuracy assessed

A Long-Term Experimental Investigation on the Impact of Rainfall on Short 6G D-Band Links

Results from a long-term propagation campaign are presented, whose main goal is to investigate the impact of rainfall on short terrestrial links operating at frequencies in the D-band, to be possibly exploited for backhaul links in future 6G mobile networks. To this aim, data are collected at two sites with different climatic conditions (Milan, Italy; Athens, Greece) for 24 and 20 months, respectively, using two links (path length of 325 and 100 m, respectively), operating at 156 GHz carrier frequency. At the same sites, disdrometers are also installed to concurrently collect information on precipitation, not only in terms of rain rate but also of its microphysical properties. The received power data are carefully pre-processed to exclude outliers and further elaborated to derive the rain attenuation. The data are afterward used to evaluate the accuracy of different prediction models, both on an event basis and on a statistical basis. Results indicate that the information delivered by the Drop Size Distribution allows a more accurate estimation of the rain attenuation and that the model currently adopted by the ITU-R to predict rain attenuation statistics on terrestrial links (recommendation ITU-R P.530-18) yields a significant overestimation for such short links, due to the unrealistic value of its path reduction factor. On the contrary, the statistical prediction model proposed by Lin turns out to offer a very satisfactory prediction accuracy

Rain Effects on FSO and mmWave Links: Preliminary Results from an Experimental Study

Optical and mmWave terrestrial links are somewhat considered complementary as they have a different sensitivity to fog and rain, i.e. the most frequent atmospheric impairments at mid-latitude. Hence, hybrid optical-mmWave systems that back-up each other according to weather conditions, have been proposed as they put together extremely large-bandwidth and high availability. However, in order to assess whether optical and mmWave systems can be considered complementary rather than competitors, the propagation effects should be quantified, possibly on a statistical basis. This paper presents preliminary results of the effects of rain on a commercial optical link at 1550 nm and a co-located dual-band mmWave link. It is shown that the degradation of the optical signal is not always well correlated with the microphysical properties of rain, Signal attenuation can be substantially underestimated if predicted by the electromagnetic theory, due to the concurrent action of other factors