During the past three years the Institute for Fluid Power Drives and Controls in Aachen has developed a new hydraulic system for mobile machinery called STEAM. The system represents a new step in excavator hydraulics, as it aims to reduce both the hydraulic system losses as well as those of the internal combustion engine by using a hybrid hydraulic architecture with accumulators. Starting with initial simulation studies the development has been followed by scaled test bench measurements and has progressed to a full scale validation using an 18 t excavator. The following publication aims to summarise the results obtained thus far with the aim of making them available to industry and encouraging their implementation in future applications.

No description available.

No description available.

Dynamical systems that provably satisfy given specifications have become increasingly important in many engineering areas. For instance, safety-critical systems such as human-robot networks or autonomous driving systems are required to be safe and to also satisfy some complex specifications that may include timing constraints, i.e., when or in which order some tasks should be accomplished. Temporal logics have recently proven to be a valuable tool for these control systems by providing a rich specification language. Existing temporal logic-based control approaches discretize the underlying dynamical system in space and/or time, which is commonly referred to as the abstraction process. In other words, the continuous dynamical system is abstracted into a finite system representation, e.g., into a finite state automaton. Such approaches may lead to high computational burdens due to the curse of dimensionality, which makes it hard to use them in practice. Especially with respect to multi-agent systems, these methods do not scale computationally when the number of agents increases. We will address this open research question by deriving abstraction-free control methods for single- and multi-agent systems under signal temporal logic tasks. Another aim of this research is to consider robustness, which is partly taken care of by the robust semantics admitted by signal temporal logic as well as by the robustness properties of the derived control methods. In this work, we propose computationally-efficient frameworks that deal with the aforementioned problems for single- and multi-agent systems by using feedback control strategies such as optimization-based techniques, prescribed performance control, and control barrier functions in combination with hybrid systems theory that allows us to model some higher level decision-making. In each of these approaches, the temporal properties of the employed control methods are used to impose a temporal behavior on the closed-loop system dynamics, which eventually results in the satisfaction of the signal temporal logic task. With respect to the multi-agent case, we consider a bottom-up approach where each agent is subject to a local (individual) task. These tasks may depend on the behavior of other agents. Hence, the multi-agent system is subject to couplings induced on the task level as well as on the dynamical level. The main challenge then is to deal with these couplings and derive control methods that can still satisfy the given tasks or alternatively result in least violating solutions. The efficacy of the theoretical findings is demonstrated in simulations of single- and multi-agent systems under complex specifications. / <p>QC 20180502</p>

<p>Driver Assistance Systems like Adaptive Cruise Control (ACC) can help prevent accidents by reducing the workload on the driver. However, this can only be accomplished if the driver can rely on the system to perform safely even in the presence of faults.</p> <p>In this thesis we develop an Adaptive Cruise Control model that will be used to investigate Hybrid Systems Fault Diagnosis techniques. System Identification is performed upon an electric motor to obtain its transfer function. This electric motor belongs to a 1/10th scale RC car that is being used as part of a test bench for the Adaptive Cruise Control system. The identified model is then used to design a hybrid controller which will switch between a set of LQR controllers to create an example Adaptive Cruise Controller. The model of the controller is then used to generate fixed point code for implementation on the testbed and validation against the model controller. Finally a detailed hazard analysis of the resulting system is performed using Leveson's STPA.</p> / Master of Applied Science (MASc)

This research paper focuses on analog computers and creating a modular low-cost analog computer system in a single board computer form factor. The single-board analog computer will have the capacity to solve second-order differential equations. The capabilities and possibilities of the single board Analog computer will be explored as well as analog computing in general. The paper follows design science research methodology (DSRM) with the goal of creating and evaluating a working artifact. The artifacts' functionality is evaluated based on a demonstration of its ability to solve Mathieu’s differential equation as well as simulate a spring-mass dampening system. This paper proves that it is possible to create a low-cost analog computer in a modern form factor. The artifact is also placed in a larger contextual setting based on the empirical material provided where its value of it in a digital society is presented. For the world to continue its progression in computational power, but still, limit the already high energy usage, a drastic change is needed. This paper suggests adapting to analog/hybrid technology. To further the progression of analog/hybrid technology it must be made accessible to a wider group of people compared to today. The artifact in this paper offers a solution to this.

This thesis synthesizes general and scalable distributed nonlinear control algorithms with application to legged robots. It explores both naturally decentralized problems in legged locomotion, such as the collaborative control of human-lower extremity prosthesis and the decomposition of high-dimensional controllers of a naturally centralized problem into a net- work of low-dimensional controllers while preserving equivalent performance. In doing so, strong nonlinear interaction forces arise, which this thesis considers and sufficiently addresses. It generalizes to both symmetric and asymmetric combinations of subsystems. Specifically, this thesis results in two distinct distributed control algorithms based on the decomposition approach. Towards synthesizing the first algorithm, this thesis presents a formal foundation based on de- composition, Hybrid Zero Dynamics (HZD), and scalable optimization to develop distributed controllers for hybrid models of collaborative human-robot locomotion. This approach con- siders a centralized controller and then decomposes the dynamics and parameterizes the feedback laws to synthesize local controllers. The Jacobian matrix of the Poincaré map with local controllers is studied and compared with the centralized ones. An optimization problem is then set up to tune the parameters of the local controllers for asymptotic stability. It is shown that the proposed approach can significantly reduce the number of controller parameters to be optimized for the synthesis of distributed controllers, deeming the method computationally tractable. To evaluate the analytical results, we consider a human amputee with the point of separation just above the knee and assume the average physical parameters of a human male. For the lower-extremity prosthesis, we consider the PRleg, a powered knee-ankle prosthetic leg, and together, they form a 19 Degrees of Freedom (DoF) model. A multi-domain hybrid locomotion model is then employed to rigorously assess the performance of the afore-stated control algorithm via numerical simulations. Various simulations involving the application of unknown external forces and altering the physical parameters of the human model unbeknownst to the local controllers still result in stable amputee loco- motion, demonstrating the inherent robustness of the proposed control algorithm. In the later part of this thesis, we are interested in developing distributed algorithms for the real-time control of legged robots. Inspired by the increasing popularity of Quadratic programming (QP)-based nonlinear controllers in the legged locomotion community due to their ability to encode control objectives subject to physical constraints, this thesis exploits the idea of distributed QPs. In particular, this thesis presents a formal foundation to systematically decompose QP-based centralized nonlinear controllers into a network of lower-dimensional local QPs. The proposed approach formulates a feedback structure be- tween the local QPs and leverages a one-step communication delay protocol. The properties of local QPs are analyzed, wherein it is established that their steady-state solutions on periodic orbits (representing gaits) coincide with that of the centralized QP. The asymptotic convergence of local QPs' solutions to the steady-state solution is studied via Floquet theory. Subsequently, to evaluate the effectiveness of the analytical results, we consider an 18 DoF quadrupedal robot, A1, as a representative example. The network of distributed QPs mentioned earlier is condensed to two local QPs by considering a front-hind decomposition scheme. The robustness of the distributed QP-based controller is then established through rigorous numerical simulations that involve exerting unmodelled external forces and intro- ducing unknown ground height variations. It is further shown that the proposed distributed QPs have reduced sensitivity to noise propagation when compared with the centralized QP. Finally, to demonstrate that the resultant distributed QP-based nonlinear control algorithm translates equivalently well to hardware, an extensive set of blind locomotion experiments on the A1 robot are undertaken. Similar to numerical simulations, unknown external forces in the form of aggressive pulls and pushes were applied, and terrain uncertainties were introduced with the help of arbitrarily displaced wooden blocks and compliant surfaces. Additionally, outdoor experiments involving a wide range of terrains such as gravel, mulch, and grass at various speeds up to 1.0 (m/s) reiterate the robust locomotion observed in numerical simulations. These experiments also show that the computation time is significantly dropped when the distributed QPs are considered over the centralized QP. / Doctor of Philosophy / Inspiration from animals and human beings has long driven the research of legged loco- motion and the subsequent design of the robotic counterparts: bipedal and quadrupedal robots. Legged robots have also been extended to assist human amputees with the help of powered prostheses and aiding people with paraplegia through the development of exoskeleton suits. However, in an effort to capture the same robustness and agility demonstrated by nature, our design abstractions have become increasingly complicated. As a result, the en- suing control algorithms that drive and stabilize the robot are equivalently complicated and subjected to the curse of dimensionality. This complication is undesirable as failing to compute and prescribe a control action quickly destabilizes and renders the robot uncontrollable. This thesis addresses this issue by seeking nature for inspiration through a different perspective. Specifically, through some earlier biological studies on cats, it was observed that some form of locality is implemented in the control of animals. This thesis extends this observation to the control of legged robots by advocating an unconventional solution. It proposes that a high-dimensional, single-legged agent be viewed as a virtual composition of multiple, low-dimensional subsystems. While this outlook is not new and forms precedent to the vast literature of distributed control, the focus has always been on large-scale systems such as power networks or urban traffic networks that preserve sparsity, mathematically speaking. On the contrary, legged robots are underactuated systems with strong interaction forces acting amongst each subsystem and dense mathematical structures. This thesis considers this problem in great detail and proposes developments that provide theoretical stability guarantees for the distributed control of interconnected legged robots. As a result, two distinctly different distributed control algorithms are formulated. We consider a naturally decentralized structure appearing in the form of a human-lower extremity prosthesis to synthesize distributed controllers using the first control algorithm. Subsequently, the resultant local controllers are rigorously validated through extensive full- order simulations. In order to validate the second algorithm, this thesis considers the problem of quadrupedal locomotion as a representative example. It assumes for the purposes of control synthesis that the quadruped is comprised of two subsystems separated at the geometric center, resulting in a front and hind subsystem. In addition to rigorous validation via numerical simulations, in the latter part of this thesis, to demonstrate that distributed controllers preserve practicality, rigorous and extensive experiments are undertaken in indoor and outdoor settings on a readily available quadrupedal robot A1.

This thesis presents a solver to handle constrained-state-space ODEs. This solver locates the points where any of the states go outside of the constraining set, and then, transfers the control from the continuous time ODE to the function governing the behavior of the system on the boundaries of the constrained set. The main contribution of this solver is found simulating complex right-hand-sided ODEs for long periods of time. / Master of Science

Este trabalho apresenta o processo de ampliação da infraestrutura laboratorial de minirredes e sistemas híbridos do Laboratório de Sistemas Fotovoltaicos do Instituto de Energia e Ambiente da Universidade de São Paulo, (LSF-IEE/USP). O trabalho também contempla uma revisão do estado da arte de sistemas híbridos e minirredes, apresentando principalmente os aspectos técnicos, como formas de acoplamento, e interações com a rede elétrica de distribuição. Descrevem-se os sistemas híbridos presentes no LSF e a infraestrutura para sua interconexão. Posteriormente são realizados os processos de comissionamento e testes operacionais da interconexão dos sistemas híbridos entre si e com a rede elétrica. Ao final é proposto um curso de aperfeiçoamento em minirredes e sistemas híbridos utilizando a infraestrutura presente no LSF. / This work presents the expansion of the micro-grid and hybrid systems infrastructure at the Laboratory of Photovoltaic Systems of the Institute of Energy and Environment at the University of São Paulo (LSF-IEE / USP). The work also presents a review of the state of the art of hybrid systems and micro-grid, presenting mainly the technical aspects, such as types of system interconnections and interactions with the main grid. The hybrid systems existent in the LSF, as well as the infrastructure for their interconnection are described. Subsequently, the commissioning process and the operational tests with the interconnection of the hybrid systems with each other and with the main grid are performed. At the end, a capacity building course on micro-grids and hybrid systems using the existent infrastructure in the LSF is proposed.

Este trabalho tem como objetivo principal a proposição de um método de desenvolvimento de sistemas híbridos de planejamento e programação da produção para ambientes de manufatura enxuta que possuam alta variedade de itens, estruturas complexas, variabilidade de lead times e demanda flutuante. Nestes ambientes existe uma grande dificuldade na definição das estratégias para a adoção do sistema mais adequado de planejamento e programação da produção. A maioria das empresas acaba adotando um tratamento genérico de planejamento e programação para todos os itens. O método foi desenvolvido a partir de uma ampla revisão bibliográfica em torno de sistemas de planejamento, programação e controle da produção, de suas respectivas funções, dos desafios para os sistemas atuais, bem como dos princípios e das principais práticas e ferramentas enxutas. Em seguida, o método foi testado em quatro aplicações práticas nas quais a essência da discussão em torno de um sistema de planejamento e programação da programação migrou do tradicional conflito entre sistemas kanban versus MRP, puxar versus empurrar, para o desafio de se criar um ambiente no qual estes dois sistemas, juntamente com outros, devem coexistir em harmonia. / This work has as main goal to propose a method of developing hybrid systems for planning and scheduling for lean manufacturing environments that have high variety of items, complex structures, variability of lead times and fluctuating demand. In these environments there is great difficulty in defining the strategies to adopt the most appropriate system of planning and scheduling. Most companies just adopting a generic treatment planning and programming for all items. The method was developed from an extensive literature review around systems of planning and scheduling of production, their respective roles, the challenges to the current systems as well as the principles and practices of the major tools and dried. Then, the method was tested in four practical applications in which the essence of the debate on a system of planning and scheduling migrated from traditional conflict between kanban systems versus MRP, pull vs. push, to the challenge of creating an environment in which these two systems, along with others, must coexist in harmony.