76 research outputs found
SCALER: Versatile Multi-Limbed Robot for Free-Climbing in Extreme Terrains
This paper presents SCALER, a versatile free-climbing multi-limbed robot that
is designed to achieve tightly coupled simultaneous locomotion and dexterous
grasping. Although existing quadruped-limbed robots have shown impressive
dexterous skills such as object manipulation, it is essential to balance
power-intensive locomotion and dexterous grasping capabilities. We design a
torso linkage and a parallel-serial limb to meet such conflicting skills that
pose unique challenges in the hardware designs. SCALER employs underactuated
two-fingered GOAT grippers that can mechanically adapt and offer 7 modes of
grasping, enabling SCALER to traverse extreme terrains with multi-modal
grasping strategies. We study the whole-body approach, where SCALER uses its
body and limbs to generate additional forces for stable grasping with
environments, further enhancing versatility. Furthermore, we improve the GOAT
gripper actuation speed to realize more dynamic climbing in a closed-loop
control fashion. With these proposed technologies, SCALER can traverse
vertical, overhang, upside-down, slippery terrains, and bouldering walls with
non-convex-shaped climbing holds under the Earth's gravity
First Steps Towards Full Model Based Motion Planning and Control of Quadrupeds: A Hybrid Zero Dynamics Approach
The hybrid zero dynamics (HZD) approach has become a powerful tool for the gait planning and control of bipedal robots. This paper aims to extend the HZD methods to address walking, ambling and trotting behaviors on a quadrupedal robot. We present a framework that systematically generates a wide range of optimal trajectories and then provably stabilizes them for the full-order, nonlinear and hybrid dynamical models of quadrupedal locomotion. The gait planning is addressed through a scalable nonlinear programming using direct collocation and HZD. The controller synthesis for the exponential stability is then achieved through the Poincaré sections analysis. In particular, we employ an iterative optimization algorithm involving linear and bilinear matrix inequalities (LMIs and BMIs) to design HZD-based controllers that guarantee the exponential stability of the fixed points for the Poincaré return map. The power of the framework is demonstrated through gait generation and HZD-based controller synthesis for an advanced quadruped robot, —Vision 60, with 36 state variables and 12 control inputs. The numerical simulations as well as real world experiments confirm the validity of the proposed framework
In silico case studies of compliant robots: AMARSI deliverable 3.3
In the deliverable 3.2 we presented how the morphological computing ap-
proach can significantly facilitate the control strategy in several scenarios,
e.g. quadruped locomotion, bipedal locomotion and reaching. In particular,
the Kitty experimental platform is an example of the use of morphological
computation to allow quadruped locomotion. In this deliverable we continue
with the simulation studies on the application of the different morphological
computation strategies to control a robotic system
Walking and Running with StarlETH
This paper presents the latest advances we made in static and dynamic locomotion with our compliant quadrupedal robot StarlETH. It summarizes the robot design and outlines the different underlying control principles used to achieve sophisticated locomotion performance. The focus of the paper is put on experimental findings which illustrate that the applied actuation and control principles are a valuable approach to bring our robotic devices a step closer to their natural counterparts
An online learning algorithm for adapting leg stiffness and stride angle for efficient quadruped robot trotting
Animals adjust their leg stiffness and stride angle in response to changing ground conditions and gait parameters, resulting in improved stability and reduced energy consumption. This paper presents an online learning algorithm that attempts to mimic such animal behavior by maximizing energy efficiency on the fly or equivalently, minimizing the cost of transport of legged robots by adaptively changing the leg stiffness and stride angle while the robot is traversing on grounds with unknown characteristics. The algorithm employs an approximate stochastic gradient method to change the parameters in real-time, and has the following advantages: (1) the algorithm is computationally efficient and suitable for real-time operation; (2) it does not require training; (3) it is model-free, implying that precise modeling of the robot is not required for good performance; and (4) the algorithm is generally applicable and can be easily incorporated into a variety of legged robots with adaptable parameters and gaits beyond those implemented in this paper. Results of exhaustive performance assessment through numerical simulations and experiments on an under-actuated quadruped robot with compliant legs are included in the paper. The robot platform used a pneumatic piston in each leg as a variable, passive compliant element. Performance evaluation using simulations and experiments indicated that the algorithm was capable of converging to near-optimal values of the cost of transport for given operating conditions, terrain properties, and gait characteristics with no prior knowledge of the terrain and gait conditions. The simplicity of the algorithm and its demonstrably improved performance make the approach of this paper an excellent candidate for adaptively controlling tunable parameters of compliant, legged robots
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
A Novel Lockable Spring-loaded Prismatic Spine to Support Agile Quadrupedal Locomotion
This paper introduces a way to systematically investigate the effect of
compliant prismatic spines in quadrupedal robot locomotion. We develop a novel
spring-loaded lockable spine module, together with a new Spinal
Compliance-Integrated Quadruped (SCIQ) platform for both empirical and
numerical research. Individual spine tests reveal beneficial spinal
characteristics like a degressive spring, and validate the efficacy of a
proposed compact locking/unlocking mechanism for the spine. Benchmark vertical
jumping and landing tests with our robot show comparable jumping performance
between the rigid and compliant spines. An observed advantage of the compliant
spine module is that it can alleviate more challenging landing conditions by
absorbing impact energy and dissipating the remainder via feet slipping through
much in cat-like stretching fashion.Comment: To appear in 2023 IEEE IRO
Frequency-Aware Model Predictive Control
Transferring solutions found by trajectory optimization to robotic hardware
remains a challenging task. When the optimization fully exploits the provided
model to perform dynamic tasks, the presence of unmodeled dynamics renders the
motion infeasible on the real system. Model errors can be a result of model
simplifications, but also naturally arise when deploying the robot in
unstructured and nondeterministic environments. Predominantly, compliant
contacts and actuator dynamics lead to bandwidth limitations. While classical
control methods provide tools to synthesize controllers that are robust to a
class of model errors, such a notion is missing in modern trajectory
optimization, which is solved in the time domain. We propose frequency-shaped
cost functions to achieve robust solutions in the context of optimal control
for legged robots. Through simulation and hardware experiments we show that
motion plans can be made compatible with bandwidth limits set by actuators and
contact dynamics. The smoothness of the model predictive solutions can be
continuously tuned without compromising the feasibility of the problem.
Experiments with the quadrupedal robot ANYmal, which is driven by
highly-compliant series elastic actuators, showed significantly improved
tracking performance of the planned motion, torque, and force trajectories and
enabled the machine to walk robustly on terrain with unmodeled compliance
Free-Standing Leaping Experiments with a Power-Autonomous, Elastic-Spined Quadruped
We document initial experiments with Canid, a freestanding, power-autonomous quadrupedal robot equipped with a parallel actuated elastic spine. Research into robotic bounding and galloping platforms holds scientific and engineering interest because it can both probe biological hypotheses regarding bounding and galloping mammals and also provide the engineering community with a new class of agile, efficient and rapidly-locomoting legged robots. We detail the design features of Canid that promote our goals of agile operation in a relatively cheap, conventionally prototyped, commercial off-the-shelf actuated platform. We introduce new measurement methodology aimed at capturing our robot’s “body energy” during real time operation as a means of quantifying its potential for agile behavior. Finally, we present joint motor, inertial and motion capture data taken from Canid’s initial leaps into highly energetic regimes exhibiting large accelerations that illustrate the use of this measure and suggest its future potential as a platform for developing efficient, stable, hence useful bounding gaits.
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