Lateral Wind Estimation and Backstepping Compensation for Safer Self-Driving Racecars

This paper addresses the lateral wind gust estimation and compensation problem for racecar models. A wind-sensorless solution, i.e. a solution not using direct wind measures, is proposed. More precisely, by modeling the wind disturbance as a fully unknown input signal, an input-state observer is derived using only information about the vehicle’s longitudinal speed and lateral pose relative to the road. The observer is characterized by a simple structure, explicit closed-form, direct implementability on a micro-controller, and dead-beat property, i.e. it ensures the convergence of the estimation error in a finite time. Moreover, leveraging on the reconstructed wind data, a backstepping wind-compensation controller is also proposed, allowing asymptotic tracking of a path with desired curvature and providing the end-user with a free control parameter specifying the desired tracking speed. Formal proofs of the estimation error and tracking error convergence are given. Performance evaluation of the proposed solution is obtained in simulation by closing in the loop the full nonlinear model of a real racecar, the Robocar system, with the proposed estimation and control method. Both the estimator and the controller are shown to outperform existing solutions, even in the presence of noisy measurements

A quick method for Bond work index approximate value determination

The Bond work index is a measure of ore resistance to crushing and grinding and is determined using the Bond grindability test. Its value constitutes ore characteristic and is used for industrial comminution plants designing. Determining the Bond work index value is quite complicated, time-consuming and requires trained operating personnel and therefore is subjected to errors. A quick method for the Bond work index approximate value determination, which is based on the first order grinding kinetics, is presented in this paper. Comparative experiments for the Bond work index value determination using the standard and quick procedures were carried out on samples of limestone and andesite, and on composite samples containing both ores in different mass proportions. This quick procedure can be performed with an arbitrary number of milling cycles, depending on the desired accuracy

Toner recovery from suspensions with fiber and comparative analysis of two kinetic models

This paper studies kinetic aspects of toner flotation in a mechanical cell with methyl isobutyl carbinol (MIBC) as a frother by using a synthetic toner sample 212+0 μm in a size at variable pH. The effect of the MIBC dosage and pH value on the flotation behavior of the toner has been investigated in terms of toner recovery and fiber recovery. Two kinetic models, the classical first order model and a modified first order model, have been tested and compared. It was established that the achieved optimal parameters of flotation were MIBC 1.5 mg/dm3 and pH from 7 to 12. The obtained results indicate that the toner floats rapidly and that flotation kinetics fits well the modified first order model with a very good correlation coefficient compared to the correlation coefficient for the classical first order model

Decoupled nonlinear adaptive control of position and stiffness for pneumatic soft robots

This article addresses the problem of simultaneous and robust closed-loop control of joint stiffness and position, for a class of antagonistically actuated pneumatic soft robots with rigid links and compliant joints. By introducing a first-order dynamic equation for the stiffness variable and using the additional control degree of freedom, embedded in the null space of the pneumatic actuator matrix, an innovative control approach is introduced comprising an adaptive compensator and a dynamic decoupler. The proposed solution builds upon existing adaptive control theory and provides a technique for closing the loop on joint stiffness in pneumatic variable stiffness actuators. Under a very mild assumption involving the inertia and actuator matrices, the solution is able to cope with uncertainties of the model and, when the desired stiffness is constant or slowly varying, also of the pneumatic actuator. Position and stiffness decoupling is achieved by the introduction of a first-order differential equation for an internal state variable of the controller, which takes into account the time derivative of pressure in the stiffness dynamics. A formal proof of the stability of the position and stiffness tracking errors is provided. An appealing property of the approach is that it does not require higher derivatives of position or any derivatives of stiffness. The solution is validated with respect to several use-cases, first in simulation and then via a real pneumatic soft robot with McKibben muscles. A comparison with respect to existing techniques reveals a more robust position and stiffness tracking skill

Force/Torque-Sensorless Joint Stiffness Estimation in Articulated Soft Robots

Currently, the access to the knowledge of stiffness values is typically constrained to a-priori identified models or datasheet information, which either do not usually take into ac- count the full range of possible stiffness values or need extensive experiments. This work tackles the challenge of stiffness estimation in articulated soft manipulators, and it proposes an innovative solution adding value to the previous research by removing the necessity for force/torque sensors and generalizing to multi-degree- of-freedom robots. Built upon the theory of unknown input-state observers and recursive least-square algorithms, the solution is independent of the actuator model parameters and its internal control signals. The validity of the approach is proven analytically for single and multiple degree-of-freedom robots. The obtained estimators are first evaluated via simulations on articulated soft robots with different actuations and then tested in experiments with real robotic setups using antagonistic variable stiffness actuators

On the stability of the soft pendulum with affine curvature: open-loop, collocated closed-loop, and switching control

This letter investigates the stability properties of the soft inverted pendulum with affine curvature - a tem- plate model for nonlinear control of underactuated soft robots. We look at how changes in physical parameters affect stability and equilibrium. We give conditions under which zero dynamics corresponding to a collocated choice of the output is (locally or globally) stable or unstable. We leverage these results to design a switching controller that stabilizes a class of nonlinear equilibria of the pendulum, which can drive the system from one equilibrium to another