Shared Control Policies and Task Learning for Hydraulic Earth-Moving Machinery

This thesis develops a shared control design framework for improving operator efficiency and performance on hydraulic excavation tasks. The framework is based on blended shared control (BSC), a technique whereby the operator’s command input is continually augmented by an assistive controller. Designing a BSC control scheme is subdivided here into four key components. Task learning utilizes nonparametric inverse reinforcement learning to identify the underlying goal structure of a task as a sequence of subgoals directly from the demonstration data of an experienced operator. These subgoals may be distinct points in the actuator space or distributions overthe space, from which the operator draws a subgoal location during the task. The remaining three steps are executed on-line during each update of the BSC controller. In real-time, the subgoal prediction step involves utilizing the subgoal decomposition from the learning process in order to predict the current subgoal of the operator. Novel deterministic and probabilistic prediction methods are developed and evaluated for their ease of implementation and performance against manually labeled trial data. The control generation component involves computing polynomial trajectories to the predicted subgoal location or mean of the subgoal distribution, and computing a control input which tracks those trajectories. Finally, the blending law synthesizes both inputs through a weighted averaging of the human and control input, using a blending parameter which can be static or dynamic. In the latter case, mapping probabilistic quantities such as the maximum a posteriori probability or statistical entropy to the value of the dynamic blending parameter may yield a more intelligent control assistance, scaling the intervention according to the confidence of the prediction. A reduced-scale (1/12) fully hydraulic excavator model was instrumented for BSC experimentation, equipped with absolute position feedback of each hydraulic actuator. Experiments were conducted using a standard operator control interface and a common earthmoving task: loading a truck from a pile. Under BSC, operators experienced an 18% improvement in mean digging efficiency, defined as mass of material moved per cycle time. Effects of BSC vary with regard to pure cycle time, although most operators experienced a reduced mean cycle time

Learning and Reacting with Inaccurate Prediction: Applications to Autonomous Excavation

Motivated by autonomous excavation, this work investigates solutions to a class of problem where disturbance prediction is critical to overcoming poor performance of a feedback controller, but where the disturbance prediction is intrinsically inaccurate. Poor feedback controller performance is related to a fundamental control problem: there is only a limited amount of disturbance rejection that feedback compensation can provide. It is known, however, that predictive action can improve the disturbance rejection of a control system beyond the limitations of feedback. While prediction is desirable, the problem in excavation is that disturbance predictions are prone to error due to the variability and complexity of soil-tool interaction forces. This work proposes the use of iterative learning control to map the repetitive components of excavation forces into feedforward commands. Although feedforward action shows useful to improve excavation performance, the non-repetitive nature of soil-tool interaction forces is a source of inaccurate predictions. To explicitly address the use of imperfect predictive compensation, a disturbance observer is used to estimate the prediction error. To quantify inaccuracy in prediction, a feedforward model of excavation disturbances is interpreted as a communication channel that transmits corrupted disturbance previews, for which metrics based on the sensitivity function exist. During field trials the proposed method demonstrated the ability to iteratively achieve a desired dig geometry, independent of the initial feasibility of the excavation passes in relation to actuator saturation. Predictive commands adapted to different soil conditions and passes were repeated autonomously until a pre-specified finish quality of the trench was achieved. Evidence of improvement in disturbance rejection is presented as a comparison of sensitivity functions of systems with and without the use of predictive disturbance compensation

Methods and Tools to Ease the Electrification of Off-Highway Vehicles and Machinery Produced by Small and Medium-Sized Companies

Sostenibilità ambientale, emissione di gas serra, e inquinamento atmosferico sono tra i grandi driver dell’elettrificazione dei trasporti. Da questo punto di vista, l’elettrificazione dei consumi è evidente nel automotive, ma lo stesso è iniziato anche per l’industria Off-Highway. Questo passaggio è importante per lo sviluppo di nuove tecnologie, ma comporta nuove sfide. Per esempio, facilita l’insorgere di architetture e lo sviluppo di tecnologie evolutive e rivoluzionarie, favorendo la nascita di nuovi macchinari e aziende. A tal proposito, sia il mondo industriale che quello accademico hanno iniziato lo sviluppo di soluzioni elettrificate, ma con alti costi. Per le aziende medio-piccole, più sensibili al cambiamento, le risorse richieste da questo processo possono essere molto sfidanti. Molte lavorano come integratori di sistemi, cioè comprano dai fornitori componenti e sistemi stock. Al contrario, le aziende leader del mercato possono puntare su prodotti ottimizzati basati su componenti custom, rientrando dell’investimento iniziale grazie all’economia di scala. Modellistica e simulazione possono aiutare molto la progettazione a livello sistemico, ma lo sviluppo di un modello matematico non è banale. Questo processo può tuttavia essere semplificato da software di modellistica indirizzati all’ambiente industriale, specialmente per i produttori più piccoli. Modellistica e simulazione consentono il passaggio dall’approccio steady-state a transient-state, fondamentale per studiare i vantaggi dell’elettrificazione: nuove strategie di controllo, minori consumi energetici, maggior produttività, ecc. Dopo un’iniziale presentazione dell’industria, della sua storia, e delle sfide, sono presentati i componenti e le architetture principali. Sono anche mostrati i macchinari più interessanti per capire le tendenze di industria e ambiente accademico. Per esempio, si capisce che il retrofitting dei macchinari è importante per questa fase di transizione, seppur vero che possono essere applicate diverse migliorie. Per investigare quanto un software di modellistica di tipo industry-oriented sia in grado di aiutare le piccole-medie aziende del settore, un sollevatore idraulico elettrificato è creato usando Simscape. È mostrata la modellizzazione dei quattro sottosistemi principali, e i movimenti principali della macchina comparati con i dati sperimentali. Se ci si concentra sul focus di questo lavoro, simulazione e prove reali sono abbastanza vicini. Infatti, pur riconoscendo che modelli più dettagliati siano necessari per analisi più accurate, è evidente che questa tipologia di software può già essere usata per modellare sistemi complessi e prendere confidenza con alcuni risultati. Infine, due diversi approcci sono analizzati simulando il modello su un ciclo di lavoro. Innanzitutto, senza alcun cambiamento al sistema di controllo, viene proposto un valore di velocità che bilanci consumo di energia e produttività della macchina. A questo proposito, lo storico e le osservazioni empiriche del costruttore confermano tale risultato, evidenziando la buona applicabilità del modello. In secondo luogo, è implementata e simulata una nuova strategia per il controllo della velocità del motore elettrico, e i risultati mostrano una diminuzione del consumo energetico. Tuttavia, per migliorare l’accuratezza della previsione e diminuire di più i consumi, è necessario approfondire ulteriormente alcune componenti. I risultati ottenuti testimoniano quanto il sistema attuale possa essere migliorato senza cambiare alcun componente, basandosi solamente su un design di tipo transient-state, e sfruttando i vantaggi dell’elettrificazione. Inoltre, è dimostrato quanto un software di modellistica industry-oriented possa essere utile ai produttori più piccoli per affrontare meglio questa importante transizione.Environmental sustainability, greenhouse emissions, and air pollution reduction are among the major drivers for the electrification of the transport and mobility sector. Indeed, the electrification of the consumptions for the automotive industry is in broad daylight, but the same process has just started for the off-highway industry. This process enables new technologies, but it comes also with new challenges and objectives. For instance, it facilitates new off-highway architectures and the development of both incremental and disruptive technology, enabling the emergence of completely new machinery and companies too. In this regard, industry and academia have already started developing electrified solutions, but they come with high development costs. Small and medium-sized companies can be particularly sensitive to changes, and the expertise, cost, and timeframe related to this process can be extremely challenging. Many of these companies usually work as system integrators, relying on the integration and tuning of off-the-shelf components and systems. On the contrary, leading off-highway manufacturers can design more optimized machinery thanks to custom-made products, relying on the economy of scale to return on investments. Modeling and simulation can greatly help system-level design but building the mathematical model of an entire machinery is not trivial. In this regard, using industry-oriented modeling software like Simscape can simplify it, especially for small manufacturers. Indeed, modeling and simulation shift the design from steady-state design to dynamic and transient-state design, which is an essential step to investigate the potential of electrification: new control strategies, lower energy consumption, higher productivity, better forecast of the machinery hour rate, etc. After an overview of the industry, its history, and the new challenges, the main components and architectures typical of the electrification process are presented. The most interesting electrified machinery are also shown to understand the general trends of both industry and academia. In fact, this analysis shows how much retrofitting can be important for this transition to more electrified machinery, but also how many improvements can be applied. To investigate how much an industry-oriented modeling software can help small and medium-sized companies, an electrified material handler is modeled using Simscape. The modeling of the main four subsystems is presented (energy storage, electric motor, mechanics, and hydraulics), and the most important movements are compared with experimental data. While focusing on the real objectives of this work, simulation and real-world testing show a good match. Indeed, even if the modeling of other subsystems is needed for more in-depth and accurate analysis, it is shown how industry-oriented software can be used to model complex subsystems and to get sensible results. Lastly, two different approaches are analyzed by simulating the model over a personalized and realistic duty cycle. First, without changing anything of the current control strategy of the machinery, one reference velocity is proposed to balance energy consumption and productivity. The empirical results of the manufacturer of the hydraulic material handler confirm this trend, highlighting the good applicability of the model. Second, a new strategy based on the control of the electric motor speed is proposed and simulated. The results show the possibility of reducing energy consumption, but some components need to be modeled more in-depth to reach better accuracy and even lower results. Nonetheless, it proves how much the system can be improved without changing any component, by relying on transient-state design and using the additional control variables enabled by electrification. Furthermore, it is shown how much an industry-oriented modeling software can help SMEs during this important phase

Dynamical modelling of hydraulic excavator considered as a multibody system

This paper considers the development of a plane multibody mechanical model of a hydraulic excavator simultaneously containing an open kinematic chain and closed loops. The Lagrange multiplier technique is used for modelling of the constrained mechanical systems. This approach is used for working out the dynamic equations of excavator motion in the case of performing transportation and digging operations. The excavator is considered as a rigid body system and detailed governing equations of the mechanical and hydraulic systems are presented. The performed verification and a typical digging task simulation show the applicability of the model for study of the excavator motion simulation. Simulation results of the machine’s response are provided. It is shown that the digging process considerably influences the mechanical and hydraulic system parameters. Such models can be used for training simulators, sizing components and system design.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Volume 1 – Symposium

We are pleased to present the conference proceedings for the 12th edition of the International Fluid Power Conference (IFK). The IFK is one of the world’s most significant scientific conferences on fluid power control technology and systems. It offers a common platform for the presentation and discussion of trends and innovations to manufacturers, users and scientists. The Chair of Fluid-Mechatronic Systems at the TU Dresden is organizing and hosting the IFK for the sixth time. Supporting hosts are the Fluid Power Association of the German Engineering Federation (VDMA), Dresdner Verein zur Förderung der Fluidtechnik e. V. (DVF) and GWT-TUD GmbH. The organization and the conference location alternates every two years between the Chair of Fluid-Mechatronic Systems in Dresden and the Institute for Fluid Power Drives and Systems in Aachen. The symposium on the first day is dedicated to presentations focused on methodology and fundamental research. The two following conference days offer a wide variety of application and technology orientated papers about the latest state of the art in fluid power. It is this combination that makes the IFK a unique and excellent forum for the exchange of academic research and industrial application experience. A simultaneously ongoing exhibition offers the possibility to get product information and to have individual talks with manufacturers. The theme of the 12th IFK is “Fluid Power – Future Technology”, covering topics that enable the development of 5G-ready, cost-efficient and demand-driven structures, as well as individual decentralized drives. Another topic is the real-time data exchange that allows the application of numerous predictive maintenance strategies, which will significantly increase the availability of fluid power systems and their elements and ensure their improved lifetime performance. We create an atmosphere for casual exchange by offering a vast frame and cultural program. This includes a get-together, a conference banquet, laboratory festivities and some physical activities such as jogging in Dresden’s old town.:Group A: Materials Group B: System design & integration Group C: Novel system solutions Group D: Additive manufacturing Group E: Components Group F: Intelligent control Group G: Fluids Group H | K: Pumps Group I | L: Mobile applications Group J: Fundamental

Shared Control Policies and Task Learning for Hydraulic Earth-Moving Machinery

This thesis develops a shared control design framework for improving operator efficiency and performance on hydraulic excavation tasks. The framework is based on blended shared control (BSC), a technique whereby the operator’s command input is continually augmented by an assistive controller. Designing a BSC control scheme is subdivided here into four key components. Task learning utilizes nonparametric inverse reinforcement learning to identify the underlying goal structure of a task as a sequence of subgoals directly from the demonstration data of an experienced operator. These subgoals may be distinct points in the actuator space or distributions overthe space, from which the operator draws a subgoal location during the task. The remaining three steps are executed on-line during each update of the BSC controller. In real-time, the subgoal prediction step involves utilizing the subgoal decomposition from the learning process in order to predict the current subgoal of the operator. Novel deterministic and probabilistic prediction methods are developed and evaluated for their ease of implementation and performance against manually labeled trial data. The control generation component involves computing polynomial trajectories to the predicted subgoal location or mean of the subgoal distribution, and computing a control input which tracks those trajectories. Finally, the blending law synthesizes both inputs through a weighted averaging of the human and control input, using a blending parameter which can be static or dynamic. In the latter case, mapping probabilistic quantities such as the maximum a posteriori probability or statistical entropy to the value of the dynamic blending parameter may yield a more intelligent control assistance, scaling the intervention according to the confidence of the prediction. A reduced-scale (1/12) fully hydraulic excavator model was instrumented for BSC experimentation, equipped with absolute position feedback of each hydraulic actuator. Experiments were conducted using a standard operator control interface and a common earthmoving task: loading a truck from a pile. Under BSC, operators experienced an 18% improvement in mean digging efficiency, defined as mass of material moved per cycle time. Effects of BSC vary with regard to pure cycle time, although most operators experienced a reduced mean cycle time

Electrified Powertrains for a Sustainable Mobility: Topologies, Design and Integrated Energy Management Strategies

This Special Issue was intended to contribute to the sustainable mobility agenda through enhanced scientific and multi-disciplinary knowledge to investigate concerns and real possibilities in the achievement of a greener mobility and to support the debate between industry and academic researchers, providing an interesting overview on new needs and investigation topics required for future developments

Volume 3 – Conference

We are pleased to present the conference proceedings for the 12th edition of the International Fluid Power Conference (IFK). The IFK is one of the world’s most significant scientific conferences on fluid power control technology and systems. It offers a common platform for the presentation and discussion of trends and innovations to manufacturers, users and scientists. The Chair of Fluid-Mechatronic Systems at the TU Dresden is organizing and hosting the IFK for the sixth time. Supporting hosts are the Fluid Power Association of the German Engineering Federation (VDMA), Dresdner Verein zur Förderung der Fluidtechnik e. V. (DVF) and GWT-TUD GmbH. The organization and the conference location alternates every two years between the Chair of Fluid-Mechatronic Systems in Dresden and the Institute for Fluid Power Drives and Systems in Aachen. The symposium on the first day is dedicated to presentations focused on methodology and fundamental research. The two following conference days offer a wide variety of application and technology orientated papers about the latest state of the art in fluid power. It is this combination that makes the IFK a unique and excellent forum for the exchange of academic research and industrial application experience. A simultaneously ongoing exhibition offers the possibility to get product information and to have individual talks with manufacturers. The theme of the 12th IFK is “Fluid Power – Future Technology”, covering topics that enable the development of 5G-ready, cost-efficient and demand-driven structures, as well as individual decentralized drives. Another topic is the real-time data exchange that allows the application of numerous predictive maintenance strategies, which will significantly increase the availability of fluid power systems and their elements and ensure their improved lifetime performance. We create an atmosphere for casual exchange by offering a vast frame and cultural program. This includes a get-together, a conference banquet, laboratory festivities and some physical activities such as jogging in Dresden’s old town.:Group 8: Pneumatics Group 9 | 11: Mobile applications Group 10: Special domains Group 12: Novel system architectures Group 13 | 15: Actuators & sensors Group 14: Safety & reliabilit

Dynamical modelling of hydraulic excavator considered as a multibody system

Rad se bavi razvojem mehaničkog modela hidrauličnog bagera od više tijela koji u isto vrijeme sadrži otvoreni kinematički lanac i zatvorene petlje. Za modeliranje ograničenih mehaničkih sustava primijenjena je tehnika Lagrangeova faktora. Taj se pristup primjenjuje za dobivanje dinamičkih jednadžbi kretanja bagera kod obavljanja prijenosa i operacija kopanja. Bager se smatra sustavom krutog tijela i predstavljaju se detaljne jednadžbe za uređenje mehaničkih i hidrauličnih sustava. Izvršena provjera i simulacija tipičnog kopanja pokazuju primjenjivost sustava za proučavanje simulacije kretanja bagera. Daju se simulacijski rezultati reakcije stroja. Pokazano je da postupak kopanja znatno utječe na parametre mehaničkog i hidrauličkog sustava. Takvi se modeli mogu koristiti za obučavanje simulatora, dimenzioniranje sastavnih dijelova i dizajniranje sustava.This paper considers the development of a plane multibody mechanical model of a hydraulic excavator simultaneously containing an open kinematic chain and closed loops. The Lagrange multiplier technique is used for modelling of the constrained mechanical systems. This approach is used for working out the dynamic equations of excavator motion in the case of performing transportation and digging operations. The excavator is considered as a rigid body system and detailed governing equations of the mechanical and hydraulic systems are presented. The performed verification and a typical digging task simulation show the applicability of the model for study of the excavator motion simulation. Simulation results of the machine’s response are provided. It is shown that the digging process considerably influences the mechanical and hydraulic system parameters. Such models can be used for training simulators, sizing components and system design

The Working Hydraulics of Valve-Controlled Mobile Machines: Classification and Review

Productivity, reliability, controllability, flexibility and affordable costs represent key aspects in mobile machines. Additionally, due to the high fuel price and to the introduction of stringent emission regulations for diesel engines, the reduction of fuel consumption while persevering the existing performance is the current demand. In order to satisfy and maximize the above requirements, different hydraulic system architectures have been developed during the last decades. Both academia and industry have been investing considerable resources delivering numerous outcomes that require a classification. This review paper closes this gap by analyzing and classifying the working hydraulics of non-hybrid, valve-controlled mobile machines starting from the 1980s to the state-of-the-art. Hydraulic layouts are addressed and categorized by both discussing their fundamentals and evolutions, and by pointing out their pros and cons in a way to provide the readers with a comprehensive overview of the systems currently available on the market and at the research stage