A.P. Coimbra

SVR Versus Neural-Fuzzy Network Controllers for the Sagittal Balance of a Biped Robot

The real-time balance control of an eight-link biped robot using a zero moment point (ZMP) dynamic model is difficult due to the processing time of the corresponding equations. To overcome this limitation, two alternative intelligent computing control techniques were compared: one based on support vector regression (SVR) and another based on a first-order Takagi-Sugeno-Kang (TSK)-type neural-fuzzy (NF) network. Both methods use the ZMP error and its variation as inputs and the output is the correction of the robots torso necessary for its sagittal balance. The SVR and the NF were trained based on simulation data and their performance was verified with a real biped robot. Two performance indexes are proposed to evaluate and compare the online performance of the two control methods. The ZMP is calculated by reading four force sensors placed under each robots foot. The gait implemented in this biped is similar to a human gait that was acquired and adapted to the robots size. Some experiments are presented and the results show that the implemented gait combined either with the SVR controller or with the TSK NF network controller can be used to control this biped robot. The SVR and the NF controllers exhibit similar stability, but the SVR controller runs about 50 times faster.

Human Gait Acquisition and Characterization

This paper analyzes human motion, more specifically the human gait in the sagittal plane. A video camera is used to acquire images of a walking person, fitted with a set of white light-emitting diodes (LEDs). The acquired trajectories of the light points are then used to specify joint trajectories in a biped robot. To analyze the stability of the human gait, a system was also developed to acquire the center of pressure (CoP). This system uses eight force sensors, four under each foot. The influence of the human torso angle on the CoP position during walking was confirmed. Some experiments were carried out on a biped robot, and the results show that the acquired human gait can be used in a biped robot, after scale conversion.

Control of a Biped Robot With Support Vector Regression in Sagittal Plane

This paper describes the control of an autonomous biped robot that uses the support vector regression (SVR) method for its sagittal balance. This SVR uses the zero moment point (ZMP) position and its variation as input and the torso correction of the robots body as output. As the robot model used segments the robot into eight parts, it is difficult to use online. This is the main reason for using the artificial intelligence method. The SVR was trained with simulation data that was previously tested with the real robot. The SVR was found to be faster (with similar accuracy) than a recurrent network and a neuro-fuzzy control. This method is more precise than the model based on an inverted pendulum. The design of the feet is considered in terms of accommodating the force sensors used to estimate the center of pressure (CoP). The SVR was tested in the real robot using joint trajectories that are similar to those of human beings, and the results are presented.

Simulation control of a biped robot with Support Vector Regression

This paper describes the control of an autonomous biped robot that uses the Support Vector Regression (SVR) method for its longitudinal balance. This SVR uses the Zero Moment Point (ZMP) position and its variation as input and the longitudinal correction of the robots body is obtained as the output. The SVR was trained based on simulation data that was confirmed with the real robot. This method showed to be faster (with similar accuracy) than a recurrent network or a neuro-fuzzy control of the biped balance.

Transient heating and cooling analysis in an electromagnetic device

This paper is concerned with the finite element formulation of the transient heating and cooling problem in an electromagnetic device. The formulation presented is illustrated with the temperature distribution produced in a large 3-phase induction motor with a closed-air-circuit ventilation scheme under different load and coolant velocity conditions. The eddy currents and the hysteresis losses contributions due to the temperature-rise were taken into account, as well as the linear dependency of the electric resistivity with temperature. The numeric results obtained were compared with the experimental values available, showing a very close agreement. >

Adaptive PD Controller Modeled via Support Vector Regression for a Biped Robot

The real-time balance control of an eight link biped robot using a zero moment point (ZMP) dynamic model is difficult due to the processing time of the corresponding equations. To overcome this limitation, an intelligent computing control technique is used. This technique is based on support vector regression (SVR). The method uses the ZMP error and its variation as inputs, and the output is the correction of the robots torso necessary for its sagittal balance. The SVR is trained based on simulation data and their performance is verified with a real biped robot. The ZMP is calculated by reading four force sensors placed under each robots foot. The gait implemented in this biped is similar to a human gait that is acquired and adapted to the robots size. Some experiments are presented, and the results show that the implemented gait combined with the SVR controller can be used to control this biped robot. The SVR controller performs the control in 0.2 ms.

Influence of the neutral in the thermal performance of a three‐phase induction motor under unbalanced power supply using the finite element approach

In this paper the influence of the neutral in the thermal performance of a three‐phase squirrel cage induction motor fed by asymmetrical supply voltages is studied and analysed. A 2D finite element formulation was used to solve the steady‐state heat transfer problem. The eddy currents in the rotor bars were evaluated using a combined 3D finite element approach with analytical expressions. The numerical solutions are compared with measured experimental results obtained in laboratory tests for two load conditions and two unbalanced power supply situations with and without the neutral wire connected.

Linearizing electric fields with first order finite element potential solutions

Using first order triangular finite elements, the electric field values are constant in each element all over the mesh. This aspect introduces discretization errors that might be significant, and does not allow the plot of isolines of the electric field. The paper presents two algorithms developed and tested by the authors to overcome the previous difficulties, which transform the constant electric field values into linear ones. Discontinuities arising from the use of different permittivity materials are taken into account. The proposed methodologies are also applicable to other quantities besides the electric field, such as magnetic induction. >

SVR sagittal balance of a biped robot controlling the torso and ankle joint angles

This paper describes the control of an autonomous biped robot that combines the use of the torso and the ankle joints movements for its sagittal balance. The innovative characteristic of this controller is the combined use of the ankle and torso joints movements to correct the Zero Moment Point (ZMP). It is used an artificial intelligence technique, the Support Vector Regression, to control the balance of the robot. To obtain a good stable step it is very important to have a good initial legs trajectory design. Having this in mind human-based trajectories were used, leading to smaller control corrections of ankle and torso joints. Different combinations of torso and ankle joints corrections were tested for the balance control on flat horizontal and inclined surfaces and the results presented. In order to evaluate and compare the performance of the balance control methods of a biped robot two performance indexes are proposed.

EasyMAG – magnetic field toolbox calculator for electrical installation project

Purpose – This paper aims to present a software application, called EasyMAG, for simulating and calculating the magnetic field during the design of domestic/industrial electrical installations.Design/methodology/approach – From a CAD software 3D representation of the model, including the electric wiring and considering the current in the electrical circuits, the software evaluates the magnetic field intensity for power‐line frequencies at different heights.Findings – Two application examples are presented consisting of a cabling layout in a lab room with three phase illumination and power socket circuits and a computer room above a power transformer room. The results were compared with measured values showing a good agreement between them.Originality/value – Shows that with this software it is possible to anticipate areas where magnetic field values might reach abnormally high values and to analyze alternative wiring layouts in order to keep the magnetic field values as low as possible.