Ulrik Pagh Schultz

IROS Conference 2022 Conference Paper

Energy-Aware Planning-Scheduling for Autonomous Aerial Robots

• Adam Seewald
• Héctor García de Marina
• Henrik Skov Midtiby
• Ulrik Pagh Schultz

In this paper, we present an online planning-scheduling approach for battery-powered autonomous aerial robots. The approach consists of simultaneously planning a coverage path and scheduling onboard computational tasks. We further derive a novel variable coverage motion robust to air-borne constraints and an empirically motivated energy model. The model includes the energy contribution of the schedule based on an automatic computational energy modeling tool. Our experiments show how an initial flight plan is adjusted online as a function of the available battery, accounting for uncertainty. Our approach remedies possible in-flight failure in case of unexpected battery drops, e. g. , due to adverse atmospheric conditions, and increases the overall fault tolerance.

ICRA Conference 2018 Conference Paper

Adapting Parameterized Motions Using Iterative Learning and Online Collision Detection

• Johan Sund Laursen
• Lars Carøe Sørensen
• Ulrik Pagh Schultz
• Lars-Peter Ellekilde
• Dirk Kraft

Achieving both the flexibility and robustness required to advance the use of robotics in small and medium-sized productions is an essential but difficult task. A fundamental problem is making the robot run blindly without additional sensors while still being robust to uncertainties and variations in the assembly processes. In this paper, we address the use of parameterized motions suitable for blind execution and robust to uncertainties in the assembly process. Collisions and incorrect assemblies are detected based on robot motor currents while motion parameters are updated based on Bayesian Optimization utilizing Gaussian Process learning. This allows for motion parameters to be optimized using real world trials which incorporate all uncertainties inherent in the assembly process without requiring advanced robot and sensor setups. The result is a simple and straightforward system which helps the user automatically find robust and uncertainty-tolerant motions. We present experiments for an assembly case showing both detection and learning in the real world and how these combine to a robust robot system.

IROS Conference 2015 Conference Paper

Automatic error recovery in robot assembly operations using reverse execution

• Johan Sund Laursen
• Ulrik Pagh Schultz
• Lars-Peter Ellekilde

Robotic assembly tasks are in general difficult to program and require a high degree of precision. As the complexity of the task increases it becomes increasingly unlikely that tasks can always be executed without errors. Preventing errors beyond a certain point is economically infeasible, in particular for small-batch productions. As an alternative, we propose a system for automatically handling certain classes of errors instead of preventing them. Specifically, we show that many operations can be automatically reversed. Errors can be handled through automatic reverse execution of the control program to a safe point, from which forward execution can be resumed. This paper describes the principles behind automatic reversal of robotic assembly operations, and experimentally demonstrates the use of a domain-specific language that supports automatic error handling through reverse execution. Our contribution represents the first experimental demonstration of reversible computing principles applied to industrial robotics.

IROS Conference 2013 Conference Paper

Unity-link: A software-gateware interface for rapid prototyping of experimental robot controllers on FPGAs

• Anders Blaabjerg Lange
• Ulrik Pagh Schultz
• Anders Stengaard Sørensen

In experimental robotics, we are often faced with differing requirements between projects and as a project evolves, making the initial choice of technology difficult, often requiring a continuous and tedious development of the low-level parts of the robotic system. We propose the use of FPGAs as a flexible solution to these low-level issues; We here address the hitherto unresolved issue of interfacing the FPGA-based controllers to high-level robotics software running on a PC. This paper presents the Unity-Link software-gateware stack, which connects high-level software frameworks to our modular, FPGA-based generic hardware. Unity-Link provides simple, unified abstractions for quickly and easily interconnecting PC-based systems with nodes that provide hard real-time control of distributed robotic systems. Unity-Link uses a component-based modular bus structure based on open standards, and interfaces with a library of gateware components, enabling us to create complex applications quickly and efficiently. Automated code generation is used to provide convenient, application-specific interfaces to high-level robotics middleware such as ROS.

IROS Conference 2011 Conference Paper

Generalized programming of modular robots through kinematic configurations

• Mirko Bordignon
• Kasper Støy
• Ulrik Pagh Schultz

The distinctive feature of modular robots consists in their reconfigurable mechanical structure, as they are assembled on-demand from basic mechatronic units. This implies that kinematic models of the robots need to be computed on a case-by-case basis for each specific assembly, which is a manual and hence time-consuming and error-prone procedure. We propose to automate this process by automatically computing such kinematic models starting from simple descriptions of the modules and their assemblies. This automated computation is supported by our toolchain for programming arbitrary modular robots in arbitrary configurations, presented in this paper. We contribute two novel results through this approach. First, a high-level programming language that provides kinematic abstractions for arbitrary modular robots, in contrast to the robot-specific solutions currently available. Second, a programming abstraction to subsume multiple kinematically equivalent robot assemblies into a so-called kinematic configuration, hence eliminating the need to explicitly enumerate and program each of them. These contributions advance current techniques for modular robot programming by demonstrating a tool that a) targets multiple mechanical platforms, offering the first general solution for modular robot programming, and b) raises the abstraction level by allowing users to reason and program in terms of standardized kinematic models that are automatically mapped to physical robot configurations by the toolchain.

TAAS Journal 2011 Journal Article

Spatial Computing

• Jacob Beal
• Olivier Michel
• Ulrik Pagh Schultz

ICRA Conference 2010 Conference Paper

A distributed strategy for gait adaptation in modular robots

• David Johan Christensen
• Ulrik Pagh Schultz
• Kasper Støy

In this paper we study online gait optimization for modular robots. The learning strategy we apply is distributed, independent on robot morphology, and easy to implement. First we demonstrate how the strategy allows an ATRON robot to adapt to faults and changes in its morphology and we study the strategy's scalability. Second we extend the strategy to learn the parameters of gait-tables for ATRON and M-TRAN robots. We conclude that the presented strategy is effective for online learning of gaits for most types of modular robots and that learning can effectively be distributed by having independent processes learning in parallel.

ICRA Conference 2009 Conference Paper

A virtual machine-based approach for fast and flexible reprogramming of modular robots

• Mirko Bordignon
• Kasper Støy
• Ulrik Pagh Schultz

Modular robot programming spans a number of issues ranging from high-level coordination to controller distribution and update in individual modules. The latter issue has received little attention from the research community though in our experience it is one of the main factors hindering agile development and experimentation with physical robots: reprogramming tens or hundreds of modules can be a major overhead in the development process and cannot be done with traditional approaches without restarting the robot, which impedes updating a running system. We propose a solution based on a virtual machine design shaped around three core concepts: the context of a module and its role in the ensemble, the reactive nature of robot controllers, and control programs decomposable into subparts that can be dynamically and separately redefined. We show that by incorporating those concepts into the design we are able to both achieve program conciseness (thus providing fast and efficient code distribution) and program expressiveness (thus providing versatility to represent diverse control algorithms). The virtual machine is programmed in a high-level role-oriented language that allows the programmer to declaratively specify how programs are deployed in the modular robot. Our approach enables fast and incremental on-line updates, allowing the programmer to interactively experiment with the physical robots. We show how this design lends itself to an efficient implementation targeting typical resource-constrained modular robotic hardware by illustrating our prototype implementation for the ATRON self-reconfigurable robot.

IROS Conference 2009 Conference Paper

On the efficiency of local and global communication in modular robots

• Ricardo Franco Mendoza Garcia
• Ulrik Pagh Schultz
• Kasper Støy

As exchange of information is essential to modular robots, deciding between local or global communication is a common design choice. This choice, however, still lacks theoretical support.

IROS Conference 2009 Conference Paper

Robust and reversible self-reconfiguration

• Ulrik Pagh Schultz
• Mirko Bordignon
• Kasper Støy

Modular, self-reconfigurable robots are robots that can change their own shape by physically rearranging the modules from which they are built. Self-reconfiguration can be controlled by e. g. an off-line planner, but numerous implementation issues hamper the actual self-reconfiguration process: the continuous evolution of the communication topology increases the risk of communications failure, generating code that correctly controls the self-reconfiguration process is non-trivial, and hand-tuning the self-reconfiguration process is tedious and error-prone. To address these issues, we have developed a distributed scripting language that controls self-reconfiguration of the ATRON robot using a robust communication scheme that relies on local broadcast of shared state. This language can be used as the target of a planner, offers direct support for parallelization of independent operations while maintaining correct sequentiality of dependent operations, and compiles to a robust and efficient implementation. Moreover, a novel feature of this language is its reversibility: once a self-reconfiguration sequence is described the reverse sequence is automatically available to the programmer, significantly reducing the amount of work needed to deploy self-reconfiguration in larger scenarios. We demonstrate our approach with long-running (reversible) self-reconfiguration experiments using the ATRON robot and a reversible self-reconfiguration experiment using simulated MTRAN modules.

IROS Conference 2008 Conference Paper

A unified simulator for Self-Reconfigurable Robots

• David Johan Christensen
• David Brandt
• Kasper Støy
• Ulrik Pagh Schultz

Generic simulation platforms such as player/stage are an essential tool in mobile robotics, but until now no similar platforms have been available for the field of self-reconfigurable robots. We here present a generic simulation platform for modular, self-reconfigurable robots: the unified simulator for self-reconfigurable robots (USSR). USSR is based on a physics engine, allowing simulation of both self-reconfiguration and dynamic interaction with the environment. The simulator is implemented as a framework that provides numerous components that can be combined to form new or existing modular robots, allowing easy experimentation: USSR currently includes support for the ATRON, Odin, and M-TRAN modular robots.