6 research outputs found
Thrust control, stabilization and energetics of a quadruped running robot
In order to achieve powered autonomous running robots it is essential to develop efficient actuator systems, especially for generating the radial thrust in the legs. In addition, the control of the radial thrust of the legs can be a simple, effective method for stabilizing the body pitch in a running gait. This paper presents the mechanical systems, models and control strategies employed to generate and control leg thrust in the KOLT quadruped running robot. An analytical model of the electro-pneumatic leg thrusting system is presented and analyzed to evaluate its performance and to facilitate the design of control strategies. Several experiments have been conducted to estimate the energy losses and determine their origins as well as to compute the energetic efficiency of the actuation system. Two thrust control methods are also proposed and tested experimentally. The closed loop method regulates thrust through the control of the hip liftoff speed, a conceptually simple control strategy that stabilizes the body pitch in pronk and trot gaits without the need for central feedback, even on irregular terrain. The open-loop control method regulates the energy added in each hop based on the model of the actuator system. The efficacy of these models and techniques is tested in several planar trot and pronk experiments, and the results are analyzed focusing on the body stabilization, the power consumption and the energetic efficiency. © SAGE Publications 2008 Los Angeles
Cross Coupled Quadruped Robot Bounding with Leg Mass
Quadruped robots find application in military for load carrying, inspection of nuclear power plants and submarine, planetary explorations. The range and duration of these missions depend on the capability of the robot to be dynamically stable and run for many cycles.Moreover,
dynamically stable robots, unlike statically stable robots can tolerate departures of the centre of mass from the support polygon formed by the legs in contact with the ground .To achieve dynamic stability, the observation of control laws based on symmetry conditions led to the idea of physical cross coupling between legs
Fast biped walking with a neuronal controller and physical computation
Biped walking remains a difficult problem and robot models can
greatly {facilitate} our understanding of the underlying
biomechanical principles as well as their neuronal control. The
goal of this study is to specifically demonstrate that stable
biped walking can be achieved by combining the physical properties
of the walking robot with a small, reflex-based neuronal network,
which is governed mainly by local sensor signals. This study shows
that human-like gaits emerge without {specific} position or
trajectory control and that the walker is able to compensate small
disturbances through its own dynamical properties. The reflexive
controller used here has the following characteristics, which are
different from earlier approaches: (1) Control is mainly local.
Hence, it uses only two signals (AEA=Anterior Extreme Angle and
GC=Ground Contact) which operate at the inter-joint level. All
other signals operate only at single joints. (2) Neither position
control nor trajectory tracking control is used. Instead, the
approximate nature of the local reflexes on each joint allows the
robot mechanics itself (e.g., its passive dynamics) to contribute
substantially to the overall gait trajectory computation. (3) The
motor control scheme used in the local reflexes of our robot is
more straightforward and has more biological plausibility than
that of other robots, because the outputs of the motorneurons in
our reflexive controller are directly driving the motors of the
joints, rather than working as references for position or velocity
control. As a consequence, the neural controller and the robot
mechanics are closely coupled as a neuro-mechanical system and
this study emphasises that dynamically stable biped walking gaits
emerge from the coupling between neural computation and physical
computation. This is demonstrated by different walking
experiments using two real robot as well as by a Poincar\'{e} map
analysis applied on a model of the robot in order to assess its
stability. In addition, this neuronal control structure allows the
use of a policy gradient reinforcement learning algorithm to tune
the parameters of the neurons in real-time, during walking. This
way the robot can reach a record-breaking walking speed of 3.5
leg-lengths per second after only a few minutes of online
learning, which is even comparable to the fastest relative speed
of human walking
Energetics and Passive Dynamics of Quadruped Robot Planar Running Gaits
Quadruped robots find application in military for load carrying over uneven terrain, humanitarian
de-mining, and search and rescue missions. The energy required for quadruped robot locomotion
needs to be supplied from on-board energy source which can be either electrical batteries or fuels
such as gasolene/diesel. The range and duration of missions very much depend on the amount
of energy carried, which is highly limited. Hence, energy efficiency is of paramount importance in
building quadruped robots. Study of energy efficiency in quadruped robots not only helps in efficient
design of quadruped robots, but also helps understand the biomechanics of quadrupedal animals.
This thesis focuses on the energy efficiency of planar running gaits and presents: (a) derivation of
cost of transport expressions for trot and bounding gaits, (b) advantages of articulated torso over
rigid torso for quadruped robot, (c) symmetry based control laws for passive dynamic bounding and
design for inherent stability, and (d) effect of asymmetry in zero-energy bounding gaits
On the Stable Passive Dynamics of Quadrupedal Running
Abstract- In this paper, we study the passive dynamics of quadrupedal bounding, based on a simplified model of our Scout II quadruped robot. Surprisingly, numerical return map studies reveal that passive generation of a large variety of cyclic bounding motion is possible. Most strikingly, local stability analysis shows that the dynamics of the open loop passive system alone can confer stability of the motion! Stability improves at higher speeds, which is in agreement with recent results from biomechanics. These results can be used in developing a general control methodology for legged robots, resulting from the synthesis of feed-forward and feedback models that take advantage of the mechanical system, and might explain the success of simple, open loop bounding controllers on our experimental robot. I