Omnidirectional locomotion in a quadruped robot : a CPG-based approach

Quadruped locomotion on rough terrain and un- predictable environments is still a challenge, where the concept of Central Pattern Generators (CPG) has brought interesting ideas. In this contribution we present a CPG design based on coupled oscillators, generating the required stepping movements of a limb for omnidirectional motion. Movements are on- line modulated through small value changes in the CPG’s parameters as required to perform the desired omnidirectional locomotion in a quadruped robot. We also present a method- ology to modulate the CPG’s parameters, reducing the control dimensionality, described in terms of the robot’s translational speed, angular velocity and walking orientation. Results show the proposed controller is well suited for the online generation and modulation of the motor patterns required to achieve the desired omnidirectional walking motion

Gait transition and modulation in a quadruped robot : a brainstem-like modulation approach

In this article, we propose a bio-inspired architecture for a quadruped robot that is able to initiate/stop locomotion; generate different gaits, and to easily select and switch between the different gaits according to the speed and/or the behavioral context. This improves the robot stability and smoothness while locomoting. We apply nonlinear oscillators to model Central Pattern Generators (CPGs). These generate the rhythmic locomotor movements for a quadruped robot. The generated trajectories are modulated by a tonic signal, that encodes the required activity and/or modulation. This drive signal strength is mapped onto sets of CPG parameters. By increasing the drive signal, locomotion can be elicited and velocity increased while switching to the appropriate gaits. This drive signal can be specified according to sensory information or set a priori. The system is implemented in a simulated and real AIBO robot. Results demonstrate the adequacy of the architecture to generate and modulate the required coordinated trajectories according to a velocity increase; and to smoothly and easily switch among the different motor behaviors.The authors gratefully acknowledge Keir Pearson for all the discussions and help. This work is funded by FEDER Funding supported by the Operational Program Competitive Factors COMPETE and National Funding supported by the FCT - Foundation for Science and Technology through project PTDC/EEACRO/100655/2008

Robot phase entrainment on quadruped CPG controller

Central Pattern Generators are used in several kinds of robot locomotion, from swimming and flying, to bipeds, quadrupeds and hexapods. It is thought that this approach can yield better results in dynamical and natural environments. In this work we expand a previous quadruped locomotion controller and propose a method to couple the step cycle phase onto the locomotor CPG of a quadruped robot, creating a feedback pathway to coordinate the phases of each leg to the phase of the step cycle. This approach is tested in a simulated quadruped robot and the performed locomotion is evaluated. Results demonstrate that the proposed phase coupling synchronizes the swing step phase of ipsilateral legs to the respective step phase of the cycle and show an improvement in stability of the performed walk gait.(undefined

Hexapod locomotion : a nonlinear dynamical systems approach

The ability of walking in a wide variety of terrains is one of the most important features of hexapod insects. In this paper we describe a bio-inspired controller able to generate locomotion and switch between different type of gaits for an hexapod robot. Motor patterns are generated by coupled Central Pattern Generators formulated as nonlinear oscillators. These patterns are modulated by a drive signal, proportionally changing the oscillators frequency, amplitude and the coupling parameters among the oscillators. Locomotion initiation, stopping and smooth gait switching is achieved by changing the drive signal. We also demonstrate a posture controller for hexapod robots using the dynamical systems approach. Results from simulation using a model of the Chiara hexapod robot demonstrate the capability of the controller both to locomotion generation and smooth gait transition. The postural controller is also tested in different situations in which the hexapod robot is expected to maintain balance. The presented results prove its reliability

A bio-inspired postural control for a quadruped robot : an attractor-based dynamic

Postural stability is a requirement for autonomous adaptive legged locomotion. Neurobiological research lead to the idea that there are independent central systems for posture and locomotion, which interact when required. In this work we propose a posture control system focused in the standing posture context. We integrate the proposed posture system with a CPG design based on coupled nonlinear oscillators. The proposed system generates movements for posture correction which are modulated according to sensory information. We integrate several different responses that individually contribute to the posture equilibrium. This coordination, competition and redundancy among the responses is a key element for adaptive, flexible and fault tolerant motor system. The control system is validated through a few experiments, where the robot is subjected to different posture situations ranging from roll and pitch variations to loss of feet support

Portugal na rota do Tráfico de Seres Humanos

Portugal na rota do Tráfico de Seres Humano

Induction coil gun

This paper describes a device capable of throwing metal rings at a range of a few meters. Part of an iron pipe is inserted on a coil. A conducting non-ferromagnetic ring is inserted in the pipe through its other extremity. An alternating current flowing through the coil creates an alternating magnetic field, which magnetizes the iron pipe. So, an alternating magnetic field is created around the pipe and induces a circumferential current flowing in the ring. This current is repelled by the magnetic field, forcing the ring to jump out of the pipe

Generating trajectories with temporal constraints for an autonomous robot

Trajectory modulation and generation are two fundamental issues in the path planning problem in autonomous robotics, specially considering temporal stabilization of the generated movements. This is a very critical issue in several robotic tasks including: catching, hitting, and human-robot scenarios. In this work, we address these problems and focus on generating movement for a mobile robot, whose goal is to reach a target within a constant time. We use an Hopf oscillator whose solution controls velocity, adapted according to temporal feedback. We have also proposed an adaptive mechanism for frequency modulation of the velocity profile that enables setting different times for acceleration and deceleration. This approach is demonstrated on a DRK8000 mobile robot in order to confirm the system’s reliability with low-level sensors.(undefined

Timed trajectory generation for a toy-like wheeled robot

In this work, we address temporal stabilization of generated movements in autonomous robotics. We focus on generating movement for a mobile robot, that must reach a target location within a constant time. Target location is online calculated by using the robot visual system, such that action is steered by the sensory information. This is a very critical issue in several robotic tasks including: catching, hitting, and humanrobot scenarios. Robot velocity is controlled through an Hopf oscillator, adapted according to temporal feedback. Timing of the velocity profile is modulated according to an adaptive mechanism that enables setting different times for acceleration and deceleration. Results on a DRK8000 mobile robot confirm the system’s reliability with low-level sensors

Trends in mortality from pulmonary tuberculosis before and after antibiotics in the Portuguese sanatorium Carlos Vasconcelos Porto (1918-1991): archival evidence and its paleopathological relevance

The comparative study of patients’ profiles and outcomes from pulmonary tuberculosis (TB), before and after the discovery of antibiotic therapy, using sanatoria archives is an unexplored approach in paleopathology. Although higher mortality rates are assumed before chemotherapy, scarce information exists regarding the disease’s duration in institutionalized patients and to what extent tuberculous sufferers lived enough to develop skeletal lesions. To fill this gap, 315 clinical files from the former male Sanatorium Carlos Vasconcelos Porto, located in São Brás de Alportel, Portugal, were studied. Two periods of hospitalization were considered: 1931-1944 (n=128, Group 1) and 1955-1961 (n=187, Group 2). The average duration of hospitalization (350.3 days for Group 1 and 371.8 for Group 2) and the crude mortality (18.2% and 11.2%, respectively in Groups 1 and 2) did not differ significantly between groups. However, Cox’s regression revealed significant differences between survival curves, after adjusting for age at admission (14-74 years old), with pre-chemotherapy patients presenting a higher risk of dying during hospitalization (p=0.37, hazard ratio=1.94, IC95%=1.03-3.63). This study also confirms poorer prognoses for pulmonary tuberculosis sufferers hospitalized in sanatoria before antibiotics and reveals that a significant number of patients survived enough time to develop bone lesions