Requirement derivation method for a legged robot with series-elastic actuators

In this work we propose a new methodology for requirement derivation of the dynamical requirements of a series elastic actuator applied to a legged robot. The leg model consists of a mechanism composed of three links – representing the thigh, the shin and the foot – and two Series Elastics Actuators (SEA) – representing the knee and ankle. The stance phase of a running gait is modeled according to the Spring Loaded Inverted Pendulum (SLIP) method. To make sure that sufficient extent of running patterns is covered, the SLIP parameters are sampled inside a predefined range using the Improved Distributed Hypercube Sampling method. The number of samples used in this study is selected through a convergence test. The leg performance is then studied through a comparison between the CoM trajectory obtained simulating the mechanism with ideal actuators on its joints and with SEAs. A closed loop Impedance Controller is used to calculate the torque required by each joint that allows the system to behave as a spring, thus mimicking the spring-like behavior of the leg during the SLIP movement. The SEAs are modeled by a parametric transfer function that is also presented in this work. To the best of our knowledge, this work is the first to propose a method that accounts for the performance of this task execution.

Flow Visualization of Pipe Flows Obtained by MR Imaginary

In this study, magnetic resonance imaging (MRI), a noninvasive medical diagnostic imaging technique, was evaluated as a noncontact measurement method for fluid machinery. In this report, various simple flow fields are investigated, and a labeled water mass is tracked and visualized in two-dimensional images by the time–spatial labeling inversion pulse (time-SLIP) method. In this article, steady and pulsating pipe flows in a straight tube and in abruptly contracting and expanding channels were tested and compared with particle image velocimetry measurements or numerical simulations to evaluate their validity. In addition, as feasibility test, a rotating water turbine and a fluidic diode with a strong swirling flow were tested to estimate this method’s applicability to fluid machines. The results indicate that the time-SLIP method of tracking labeled water mass is sufficiently accurate for use in simple fluid machinery with slow flows.

CONSTANT SLIP CONTROL SYSTEM OF AN ASYNCHRONOUS MOTOR / PASTOVAUS SLYDIMO ASINCHRONINIO ELEKTROS VARIKLIO ROTORIAUS GREIČIO VALDYMO METODAS

Asynchronous motors are efficiently controlled using the scalar method. Main problems appear when the motor is fully loaded and desired rotation speed is slow. In such cases, the motor slip exceeds the magnitude of the nominal slip, causing the increase in stator current. The constant slip method was designed to control hardly loaded asynchronous motor. In this particular situation, the constant slip method provides a better efficiency than the scalar method. The magnitude of the motor current refers to the slip: the less is the slip, the less is the magnitude. It is impossible to find the optimal slip for minimization of current with the help of a model. Therefore, the nominal slip value was used as optimal. Article in Lithuanian. Santrauka Pasiūlytas pastovaus slydimo asinchroninio elektros variklio rotoriaus greičio valdymo metodas ištirtas modeliuojant, gauti rezultatai palyginti su skaliarinio valdymo metodo tyrimo rezultatais. Tyrimo rezultatai parodė, kad pastovaus slydimo asinchroninio variklio greičio valdymo metodas yra pranašesnis už skaliarinio valdymo metodą, kai valdomo variklio greitis yra nedidelis ir jo apkrova yra artima nominaliajai.