29 accepted papers
Existing preference optimization methods often assume scenarios where paired preference feedback (preferred/positive vs. dis-preferred/negative examples) is available. This requirement limits their applicability in scenarios where only unpaired feedback—for example, either positive or negative— is a…
This paper presents a novel nonlinear disturbance rejection approach for high precision model-based control of hydraulic robots. While most disturbance rejection approaches make use of observers, we propose a novel adaptive Unscented Kalman Filter to estimate the disturbances in an unbiased minimum-…
We present ConFusion, an open-source package for online sensor fusion for robotic applications. ConFusion is a modular framework for fusing measurements from many heterogeneous sensors within a moving horizon estimator. ConFusion offers greater flexibility in sensor fusion problem design than filter
Many real-world control problems involve both discrete decision variables – such as the choice of control modes, gear switching or digital outputs – as well as continuous decision variables – such as velocity setpoints, control gains or analogue outputs. However, when defining the corresponding opti
In this paper, we present a fully-integrated end-effector positioning system for large-scale multi-robotic setups used for non-repetitive manufacturing tasks. The system provides static and dynamic correction of the end-effector pose using an external pose tracking system. It consists of multiple mo
This paper introduces a family of iterative algorithms for unconstrained nonlinear optimal control. We generalize the well-known iLQR algorithm to different multiple shooting variants, combining advantages like straightforward initialization and a closed-loop forward integration. All algorithms have…
In this paper we present a system for the in situ33In the context of building construction, “in situ” means that fabrication takes place at the structure's final location directly on the building site. fabrication of a full-scale, load-bearing, and doubly-curved steel reinforced concrete wall. Two c…
In this letter, we present a new formulation for learning the dynamics of legged robots performing locomotion tasks. Using sensor data we learn error terms at the level of rigid body dynamics and actuation dynamics. The learning framework deals with the hybrid nature of legged systems given by diffe
We present a single trajectory optimization formulation for legged locomotion that automatically determines the gait sequence, step timings, footholds, swing-leg motions, and six-dimensional body motion over nonflat terrain, without any additional modules. Our phase-based parameterization of feet mo
In this letter, a system is presented to track the motion of a sensor-head relative to multiple objects of known geometry. Measurements from a monocular camera and an inertial measurement unit are probabilistically fused in a moving horizon estimator to obtain high-accuracy estimates. Methods for de
In this letter, we present a whole-body nonlinear model predictive control approach for rigid body systems subject to contacts. We use a full-dynamic system model which also includes explicit contact dynamics. Therefore, contact locations, sequences, and timings are not prespecified but optimized by
In this paper, we present an efficient Dynamic Programing framework for optimal planning and control of legged robots. First we formulate this problem as an optimal control problem for switched systems. Then we propose a multi-level optimization approach to find the optimal switching times and the o…
Despite the recent advances in, and the adoption of robotic technologies in the construction industry, the architectural processes which demand a high degree of geometric freedom still remain largely labour intensive and manual. This is due to the inherent difficulties in robotizing the current impl…
In this work we present a co-located task space sensing and control system designed to control the end-effector motion of a mobile manipulator in the presence of dynamic and unknown base motion. We present a method for generating end-effector motion estimates at 1 kilohertz for use in real time cont…
This work addresses the problem of kinematic trajectory planning for mobile manipulators with non-holonomic constraints, and holonomic operational-space tracking constraints. We obtain whole-body trajectories and time-varying kinematic feedback controllers by solving a Constrained Sequential Linear…
This letter combines the fast zero-moment-point approaches that work well in practice with the broader range of capabilities of a trajectory optimization formulation, by optimizing over body motion, footholds, and center of pressure simultaneously. We introduce a vertex-based representation of the s
In this paper, we present an algorithm for planning and control of legged robot locomotion. Given the desired contact sequence, this method generates gaits and dynamic motions for legged robots without resorting to simplified stability criteria. The method uses direct collocation for searching for s…
We present an algorithm that generates walking motions for quadruped robots without the use of an explicit footstep planner by simultaneously optimizing over both the Center of Mass (CoM) trajectory and the footholds. Feasibility is achieved by imposing stability constraints on the CoM related to th…
We introduce a robust control architecture for the whole-body motion control of torque controlled robots with arms and legs. The method is based on the robust control of contact forces in order to track a planned Center of Mass trajectory. Its appeal lies in the ability to guarantee robust stability…
In this letter, we present a trajectory optimization framework for whole-body motion planning through contacts. We demonstrate how the proposed approach can be applied to automatically discover different gaits and dynamic motions on a quadruped robot. In contrast to most previous methods, we do not
We present a trajectory optimization framework for legged locomotion on rough terrain. We jointly optimize the center of mass motion and the foothold locations, while considering terrain conditions. We use a terrain costmap to quantify the desirability of a foothold location. We increase the gait's…
To render a wearable robot imperceptible to a user is a very challenging control task. The constant and intrinsic interaction between robot and human, and person-dependent behaviours are the main difficulties when designing such cooperative control. In this contribution we introduce and discuss a no…
Despite the prevalent use of robotic technologies in industrial manufacturing, their use on building construction sites is still very limited. This is mainly due to the unstructured nature of construction sites and the fact that the structures built must be larger than the machines which build them.
This letter studies existing direct transcription methods for trajectory optimization applied to robot motion planning. There are diverse alternatives for the implementation of direct transcription. In this study, we analyze the effects of such alternatives when solving a robotics problem. Different
This paper presents a framework for real-time, full-state feedback, unconstrained, nonlinear model predictive control that combines trajectory optimization and tracking control in a single, unified approach. The proposed method uses an iterative optimal control algorithm, namely Sequential Linear Qu
Differential flatness is a property of certain systems that greatly simplifies the generation of optimal and dynamically feasible trajectories. Using a differentially flat model, there is no need to integrate the system dynamics to retrieve the states and the constraints of the optimization problem…
Sums-of-Squares optimization represents an important tool for the direct computation of a local Lyapunov function for a nonlinear dynamic system. Specifically, it can certify a sub-levelset of the cost-to-go from an optimal feedback controller like the Linear Quadratic Regulator (LQR), geometrically
An event-based communication framework for remote operation of a robot via a bandwidth-limited network is proposed. The robot sends state and environment estimation data to the operator, and the operator transmits updated control commands or policies to the robot. Event-based communication protocols…
In recent years impressive results have been presented illustrating the potential of quadrotors to solve challenging tasks. Generally, the derivation of the controllers involve complex analytical manipulation of the dynamics and are very specific to the task at hand. In addition, most approaches con…