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Control Implementation of Dynamic Locomotion on Compliant, Underactuated, Force-Controlled Legged Robots with Non-Anthropomorphic Design
The control of locomotion on legged robots traditionally involves a robot that takes a standard legged form, such as the anthropomorphic humanoid, the dog-like quadruped, or the bird-like biped. Additionally, these systems will often be actuated with position-controlled servos or series-elastic actuators that are connected through rigid links. This work investigates the control implementation of dynamic, force-controlled locomotion on a family of legged systems that significantly deviate from these classic paradigms by incorporating modern, state-of-the-art proprioceptive actuators on uniquely configured compliant legs that do not closely resemble those found in nature. The results of this work can be used to better inform how to implement controllers on legged systems without stiff, position-controlled actuators, and also provide insight on how intelligently designed mechanical features can potentially simplify the control of complex, nonlinear dynamical systems like legged robots. To this end, this work presents the approach to control for a family of non-anthropomorphic bipedal robotic systems which are developed both in simulation and with physical hardware. The first is the Non-Anthropomorphic Biped, Version 1 (NABi-1) that features position-controlled joints along with a compliant foot element on a minimally actuated leg, and is controlled using simple open-loop trajectories based on the Zero Moment Point. The second system is the second version of the non-anthropomorphic biped (NABi-2) which utilizes the proprioceptive Back-drivable Electromagnetic Actuator for Robotics (BEAR) modules for actuation and fully realizes feedback-based force controlled locomotion. These systems are used to highlight both the strengths and weaknesses of utilizing proprioceptive actuation in systems, and suggest the tradeoffs that are made when using force control for dynamic locomotion. These systems also present case studies for different approaches to system design when it comes to bipedal legged robots
Differentiable Compliant Contact Primitives for Estimation and Model Predictive Control
Control techniques like MPC can realize contact-rich manipulation which
exploits dynamic information, maintaining friction limits and safety
constraints. However, contact geometry and dynamics are required to be known.
This information is often extracted from CAD, limiting scalability and the
ability to handle tasks with varying geometry. To reduce the need for a priori
models, we propose a framework for estimating contact models online based on
torque and position measurements. To do this, compliant contact models are
used, connected in parallel to model multi-point contact and constraints such
as a hinge. They are parameterized to be differentiable with respect to all of
their parameters (rest position, stiffness, contact location), allowing the
coupled robot/environment dynamics to be linearized or efficiently used in
gradient-based optimization. These models are then applied for: offline
gradient-based parameter fitting, online estimation via an extended Kalman
filter, and online gradient-based MPC. The proposed approach is validated on
two robots, showing the efficacy of sensorless contact estimation and the
effects of online estimation on MPC performance.Comment: Submitted ICRA24. Video available at https://youtu.be/CuCTcmn3H-o
Code available at https://gitlab.cc-asp.fraunhofer.de/hanikevi/contact_mp
Haptic Bimanual System for Teleoperation of Time-Delayed Tasks
This paper presents a novel teleoperation system, which has been designed to address challenges in the remote control of spaceborne bimanual robotic tasks. The primary interest for designing this system is to assess and increase the efficacy of users performing bimanual tasks, while ensuring the safety of the system and minimising the user's mental load. This system consists of two seven-axis robots that are remotely controlled through two haptic control interfaces. The mental load of the user is monitored using a head-mounted interface, which collects eye gaze data and provides components for the holographic user interface. The development of this system enables the safe execution of tasks remotely, which is a critical building block for developing and deploying future space missions as well as other high-risk tasks
Push recovery with stepping strategy based on time-projection control
In this paper, we present a simple control framework for on-line push
recovery with dynamic stepping properties. Due to relatively heavy legs in our
robot, we need to take swing dynamics into account and thus use a linear model
called 3LP which is composed of three pendulums to simulate swing and torso
dynamics. Based on 3LP equations, we formulate discrete LQR controllers and use
a particular time-projection method to adjust the next footstep location
on-line during the motion continuously. This adjustment, which is found based
on both pelvis and swing foot tracking errors, naturally takes the swing
dynamics into account. Suggested adjustments are added to the Cartesian 3LP
gaits and converted to joint-space trajectories through inverse kinematics.
Fixed and adaptive foot lift strategies also ensure enough ground clearance in
perturbed walking conditions. The proposed structure is robust, yet uses very
simple state estimation and basic position tracking. We rely on the physical
series elastic actuators to absorb impacts while introducing simple laws to
compensate their tracking bias. Extensive experiments demonstrate the
functionality of different control blocks and prove the effectiveness of
time-projection in extreme push recovery scenarios. We also show self-produced
and emergent walking gaits when the robot is subject to continuous dragging
forces. These gaits feature dynamic walking robustness due to relatively soft
springs in the ankles and avoiding any Zero Moment Point (ZMP) control in our
proposed architecture.Comment: 20 pages journal pape
Aerial Robotics for Inspection and Maintenance
Aerial robots with perception, navigation, and manipulation capabilities are extending the range of applications of drones, allowing the integration of different sensor devices and robotic manipulators to perform inspection and maintenance operations on infrastructures such as power lines, bridges, viaducts, or walls, involving typically physical interactions on flight. New research and technological challenges arise from applications demanding the benefits of aerial robots, particularly in outdoor environments. This book collects eleven papers from different research groups from Spain, Croatia, Italy, Japan, the USA, the Netherlands, and Denmark, focused on the design, development, and experimental validation of methods and technologies for inspection and maintenance using aerial robots
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