Roy Featherstone

Bio-inspired knee joint mechanism for a hydraulic quadruped robot

Over the last few decades, legged robots are becoming a promising solution for rough terrain navigation, however, existing legged machines often lack versatility to perform a wide range of different gaits. To build a highly dynamic and versatile legged robot, it is essential to have lightweight legs with optimized design and suitable actuators for the desired robot performance and tasks. The design goals are to achieve (1) a wide range of motion for bigger foot workspace which will increase rough terrain walking performance by increasing the number of reachable footholds for each step, (2) optimized joint torque curve since torque output is related to joint angle if linear actuators like pistons are used. In this paper, we focus on the knee joint and propose the adaptation and optimization of the so-called isogram mechanism. It exhibits a changeable instantaneous center of rotation (CICR), similar to a human knee joint. We will show how an optimization of design parameters lead to a knee joint design that satisfies the above-mentioned goals. The main contributions of this paper are the kinematic and torque analysis of the isogram mechanism that is actuated by a linear actuator; the optimization of the mechanisms design parameters; a comparison between the proposed knee joint with the hinge-type knee joint of the quadruped robot HyQ; and experimental results of a proof-of-concept prototype leg featuring the proposed mechanism.

Balancing and hopping motion of a planar hopper with one actuator

In this paper, a new control algorithm is presented for implementing hopping and balancing motions on a planar hopping machine with a single actuated revolute joint. Starting with a simple control algorithm for balancing, it is extended to perform trajectory-tracking maneuvers, which enables it to perform the crouching, lift-off and flight phases of a single hop, as well as re-balancing after landing. Simulation results are presented showing that the control system works well, and that it is not significantly affected by small amounts of slipping between the foot and the ground.

High-slope terrain locomotion for torque-controlled quadruped robots

Research into legged robotics is primarily motivated by the prospects of building machines that are able to navigate in challenging and complex environments that are predominantly non-flat. In this context, control of contact forces is fundamental to ensure stable contacts and equilibrium of the robot. In this paper we propose a planning/control framework for quasi-static walking of quadrupedal robots, implemented for a demanding application in which regulation of ground reaction forces is crucial. Experimental results demonstrate that our 75-kg quadruped robot is able to walk inside two high-slope (

A New Nonlinear Model of Contact Normal Force

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Quantitative measures of a robot's physical ability to balance

50∘) V-shaped walls; an achievement that to the authors’ best knowledge has never been presented before. The robot distributes its weight among the stance legs so as to optimize user-defined criteria. We compute joint torques that result in no foot slippage, fulfillment of the unilateral constraints of the contact forces and minimization of the actuators effort. The presented study is an experimental validation of the effectiveness and robustness of QP-based force distributions methods for quasi-static locomotion on challenging terrain.

Development of the lightweight hydraulic quadruped robot — MiniHyQ

This paper presents an angular momentum based controller to control the balancing motion of a spatial underactuated robot with three degrees of under-actuation. The control algorithm is based on the idea of decoupling the robots motion instantaneously into bending and swivelling motions. This property of the robot is obtained by using a constant velocity joint as the 2-DoF active joint of the robot. Simulation results show the performance of the controller during some interesting motions of the robot such as straightening, crouching and reorienting motions. The last two motions, which are the results of decoupling the robots motion, are demonstrated here for the first time.

The Physics and Control of Balancing on a Point in the Plane

This paper presents a new nonlinear model of the normal force that arises during compliant contact between two spheres, or between a sphere and a flat plate. It differs from a well-known existing model by only a single term. The advantage of the new model is that it accurately predicts the measured values of the coefficient of restitution between spheres and plates of various materials, whereas other models do not.

A New Simple Model of Balancing in the Plane

In this paper, a new control algorithm based on angular momentum is presented for balancing an under-actuated planar robot. The controller is able to stabilize the robot in any unstable balanced configuration in which the robot is controllable, and also it is able to follow a class of arbitrary trajectories without losing balance. Simulation results show the good performance of the controller in balancing and trajectory tracking motions of the robot. The simulations also show that the proposed controller is robust to significant imperfections in the system, such as errors in the controller’s dynamic model of the robot and imperfections in the sensors and actuators. The new controller is compared with three existing balance controllers and is shown to equal or outperform them.