Projects and Publications
My interest in robotics are in two fields:
understanding control of elastic actuation principles and using system dynamics
to enhance a robots capabilities
create, maintain and explore the capabilities of complex robotic systems
I work at
University of Waterloo
You can contact me at
VR/Multi-view mobile teleoperation with haptic feedback
To understand how effective a user can be in teleoperating a manipulator with just a mobile phone, I have created a prototype. In this demonstration multiple pointclouds from RGB-D cameras are compressed, streamed over WebRTC to a mobile phone, and displayed in a VR environment which the user can navigate freely. By holding a latch button the motions of the phone are replicated by the robot, allowing the user to control the full 6D motion of the robots tip. To increase immersion, any measured external forces estimated by the robot are conveyed to the user by hapic and audio signals. Haptic and audio signalling are particularly interesting as they allow low-latency feedback in contrast to any visual feedback.
Workshop on the Talos humanoid robot
To improve collaboration Olivier Stasse and I organized a workshop around the Talos Humanoid Robot on the Humanoids Conference 2019. As part of the workshop preliminary results on the Talos at RoboHub were shown. The video show these current capabilities of the robot.
The slide of my presentation are available here:
Series elastic robot walking over obstacles
Robust walking on the series elastic robot C-Runner. This work combines
the use of optimization generated trajectories for walking on series-elastic
with the passivity based balancing control approach used in other projects.
Due to the mechanical robustness of the system, unexpected impacts can be
endured and the control scheme allows to robot to tackle obstacles of a
height of 25mm and more. Work done together with Henze B, Loeffl L, Leyendecker S, Ott C.
Published on Humanoids 2017.
Humanoid Robots in Aircraft Manufacturing
In this demonstration for
(a European Horizon H2020 Project)
Toro is using visual servoing to walk up to the table and bring himself into
a suitable position for grasping. The pink object (cable mounting bracket)
is located at a known position
relative to the April tag fixed to the table surface. This location is used to
to plan a path which is given to a Cartesian impedance controller controlling the hand motion
to grasp the bracket. Toro
then turns around to walk up to the airplane part. Arrived there a hand
contact is added to extend the reach of the robot to the target location
marked by the red square. In the following part the center of mass of the robot is
moved outside of the support polygon given by just the feet, making the
hand contact a requirement.
The robot attaches the (magnetic) bracket to the
airplane and returns to bipedal contact. The whole process is fully
This video is unedited and at original speed. Work done together with
Henze B, Porges O, Englsberger, Garofallo G, J, Roa MA and Ott C.
Enhancing Series Elastic Actuators with Damping
Series elastic actuators with soft springs can provide interesting
performance gains over rigid actuation. A drawback is that soft springs
also reduce the available bandwidth for controlling the link-side
position or torque. This can be remedied by adding a damper in parallel
to the elastic element.
Work done together with Kim MJ and Loeffl F.
ICRA 2017 (accepted)
submitted to IROS 2017
Test setup for new spring damper component.
C-Runner: Dynamic Walking Experiments
Published on IROS 2017. Work of my master thesis student Wojciech Turlej.
Compliant(SEA) Biped C-Runner is walking using optimized
trajectories. The model used contains the full link side dynamics and can
use arbitrary contact points. Additionally, the motor side limits are respected.
The resulting trajectory is the executed on the robot using motor-side
position control, the human in the loop stabilizes the base
(estimated human force <20 Newton).
C-Runner: Concept and Design
Published at IEEE/RAS Intl. Conference on Humanoid Robots (Humanoids) 2016:
The DLR C-Runner: Concept, Design and Experiments -
Werner A, Lakatos D, Reinecke J, Wolf S, Burger R, Gumpert T, Schmidt F, Ott C, Grebenstein M, Albu-Schaeffer A. This paper describes the idea behind the new series elastic biped C-Runner.
It documents characteristic system properties and shows early experiments.
Multi-Contact Planning and Control
Published at IEEE/RSJ Intl. Conference on Intelligent Robots and Systems (IROS) 2016:
Multi-Contact Planning and Control for a Torque-Controlled Humanoid Robot
- Werner A, Henze B, Rodriguez D, Gabaret J, Porges O and Roa MA.
The master thesis of Rodriguez D was co-supervised by me.
Toro is controlled using the Multi-Contact Balancer previously published.
The task at hand getting up the stairs is formulated as a sequence of contact
pairs. From this sequence, intermediate configurations are synthesized using
inverse kinematics. A modified Rapidly-exploring Random Tree algorithm which operates
on the manifold of the contact constraint is applied to generate a feasible
path. Planning time for this trajectory is approximately ten minutes. The
configuration space path is then heuristically converted into a trajectory.
The paper also features automatic generation of contact points from
RGBD data. The algorithm heuristically explores feasible steps leading
from the current contact set towards the goal. The approach presented
is applied to foot contacts only.
C-Runner: First Walking Experiments
Not published yet: Work with Henze B.
Compliant(SEA) Bipedal Robot C-Runner is walking using optimization generated
trajectories. The slow speed is attributed to limitations of the feed-back loop
used to control the series elastic actuators. The trajectory generation respects
all relevant for the link
side. The trajectories are locally stabilized using a variant of
the multi-contact balancing controller.
Picking Objects from a Table
Unpublished: Work with Porges O. Toro walks up to the table using visual servoing based on the
April tag mounted on the table. The blue cubes are then located based on RGBD
data, from the perceived position one is selected. Even though the redundant part of the robot
is used for grasping, not every
hand position in SE3 is feasible. From the object position, a number of
possible hand positions are computed and then verified against a reachability
map. If the configuration is reachable, an inverse kinematic is queried
to obtain the associated joint space configuration.
Generalization of Optimal Walking Trajectories
Published at IEEE/RSJ Intl. Conference on Intelligent Robots and Systems (IROS) 2015:
Generalization of Optimal Motion Trajectories for Bipedal Walking -
Werner A, Trautmann D, Lee D, Lampariello R. Trautmann D was supervised
by me during his master thesis done in a collaboration between DLR and TUM.
The figure on the right shows the difference local minima of a torque
cost-function. This work compares suitable methods for generalization of
a set of optimal trajectories and analyzes the errors in the process. Trajectories
for bipedal walking are especially interesting with this respect as constraint violations
can cause falling of the robot.
Control Applications of Toro
Published at IEEE/RAS Intl. Conference on Humanoid Robots (Humanoids) 2014:
Control applications of TORO - Torque controlled humanoid robot -
Henze B, Werner A, Roa MA, Garofalo G, Englsberger J and Ott C.
This video received the Best Paper Award in the Category Video Submission
at the IEEE/RAS Conference for Humanoid Robotics 2014
Not published. Work with Garofallo G, Turley W, Stoneman S.
Starting for a Matlab prototype
which implemented an algorithm for computing dynamics matrices, this
library was developed.
implements the basic building blocks for robotics research:
The listed features is combined to a simulation environment.
The library is implemented in Eigen, all algorithms are templated and can
be used with automatic differentiation. Simulation and on-line dynamics
are used in
various systems throughout the institute. The library is also the basis for
my motion planning works.
Forward kinematics and associated Jacobians
Computation of matrix quantities for the robotic equation of motion,
including time derivatives up to the second order
Recursive forward and inverse dynamics (including constraints)
Collision computation for primitives: Sphere, Capsule, Box based
on quadratic optimization
Realistic non-linear contact model
Self-collision avoidance for torque controlled robots using
Limited inverse kinematics solver
OpenSceneGraph based visualization
Published in Frontiers in Neurorobotics:
Stable myoelectric control of a hand prosthesis using non-linear incremental learning -
Gijsberts A, Bohra R, Sierra Gonzalez D, Werner A, Nowak M, Caputo B, Roa MA and Castellini C.
The EMG signals measured at the forearm of the operator are used to drive
the prosthetic hand mounted on the robot. A magnetic tracker measured the
6D pose of the operators lower arm which is replicated by the robot. A Cartesian
impedance controller is used and the redundancy of the robot is leverage to
obtain good tracking.
Later a bi-manual variant of this experiment followed.
Trajectory Optimization for Series Elastic Joints (SEA)
Published at IEEE Conference on Decision and Control 2014:
Trajectory Optimization for Walking Robots with Series Elastic Actuators -
Werner A, Lampariello R and Ott C.
This paper extend the previous work on optimization of trajectories
for bipedal walking robots to series elastic robots (SEA). The approach
uses a very small optimization problem as one spline function is used to
parameterize the link side and the motor side. The video shows an optimized
trajectory for an early design stage of C-Runner. The upper body tilt is due
to the mass distribution which is not adequately displayed by the visuals.
Legged Humanoid Robot from DLR
Published at IEEE/RAS Intl. Conference on Humanoid Robots (Humanoids) 2014.
Englsberger J, Werner A, Ott C, Henze B, Roa MA, Garofalo G,
Burger R, Beyer A, Eiberger O, Schmid K, Albu-Schaeffer A. -
Overview of the torque-controlled humanoid robot TORO. The paper summarizes
the hardware design of Toro.
Christmas Videos with Toro, DEOS and HMI
Unpublished (shown at the Christmas party of the institute): Humanoid Toro
explores the lab at night. Contributors:
Werner A, de Stefano M,
Henze B, Radhakrishna R, Porges O, Englsberger J, Ott C, Artigas J
and Roa MA.
Toro walks and displays first capabilities in tele-operation with force-feedback.
Afterwards he opens the gate and frees the locked up robots.
DLR Biped Walking using Optimal Trajectories
Published at IEEE/RSJ Intl. Conference on Intelligent Robots and Systems (IROS) 2012:
Optimization-based generation and experimental validation of
optimal walking trajectories for biped robot -
Werner A, Lampariello R and Ott C.
This paper transfers an approach for dynamic ball catching for robots
to bipedal walking. This publication sums up the work I did in my diploma
thesis supervised by my co-authors.