Advanced hydraulic systems for next generation of skid steer loaders

Fluid power systems have been extensively used in off highway applications like skid steer loaders, wheel loaders, excavators since many years. Work has been done by both industry and academia to improve efficiency, reduce noise and leakages in these systems. With increasing competition in the market, importance is now also given to operator comfort and machine productivity in off highway applications. Mobile, off – highway vehicles like Skid-steer loaders are widely used in labour saving applications like loading earth into a truck, dig and move material on construction sites to, clean roads, clear snow from roads etc. To carry out these jobs in limited spaces, skid steer loaders need tight turning radius. For this reason, these machines have a short wheelbase which prevents the use of suspensions in these vehicles. The absence of a suspension system exposes the vehicle to ground vibrations of high magnitude and low frequency. Vibrations reduce operator comfort, productivity and life of components. This thesis will discuss control strategies for vibration damping of skid steer loader using the hydraulic boom cylinder as the active suspension element, which is equivalent to a spring–damper. Along with vibrations, the machine productivity is also hampered by material spillage which is caused by the tilting of the bucket due to the extension of the boom. This dissertation will discuss the development of a robust path-planning control algorithm which adapts to the position of the boom to maintain a level load to achieve bucket self-leveling. Another reason for reduced productivity in skid steer loaders is slow in site travel speeds. This dissertation also concentrates on reducing the in-job cycle time by developing a control strategy to smooth speed shift the drive motors keeping the pump flow constant. To synthesize these proposed control algorithms, high fidelity hydraulic and mechanical models of the skid steer loader are created. Ultimately, the control algorithms derived in this dissertation help in improving operator comfort and machine productivity

Reinforcement learning: a control approach for reducing component damage in mobile machines

This paper presents an active component damage reducing control approach for driving manoeuvres of a wheel loader. For this purpose, the front and rear axle loads will be manipulated by force pulses induced into the machine chassis via the lifting cylinders of the function drive. The associated control approach is based on the principles of Reinforcement Learning. The essential advantage of such methods against linear control approaches is that no descriptive system properties are required, but the algorithm automatically determines the system behaviour. Due to the high number of necessary training runs, the algorithm is designed and taught using a validated wheel loader simulation model. After over 850 training runs, an optimal strategy for damping the axle loads could not yet be determined. In spite of the unprecedented convergence, initial improvements of the damage values have already been achieved on tracks that deviate from the training track. Some of these results show a 4.9 % lower component damage compared to a machine setting with no damping system. The results and limits of this strategy are discussed due to a comparison with other scientific active vibration damping approaches. Currently, a linear control method (P-PI-controller) has a higher damage reduction potential, but it is expected that further training runs and another learning algorithm could make the reinforcement learning approach even more effective. Coupling the linear control method with the selflearning approach shows the highest potential for the axle damage reduction

Efficient simulation of Mechanism Kinematics Using Bond Graphs.

This paper presents a methodology for obtaining the equations corresponding to a mechanism that are necessary for carrying out a kinematic simulation. A simulation of this kind means obtaining the coordinates dependent on the system according to the movements imposed by the degrees of freedom. Unlike a dynamic simulation, where the set of elements moves according to the different external forces existing, in kinematic simulation the movement of the whole set depends exclusively on imposing movement on one or more of the bodies according to the degrees of freedom initially possessed by the mechanism. After presenting an analysis of how to obtain the necessary equations for several simple systems, this methodology is applied to the particular case of a front-loader, where in order to move and tilt the bucket, various closed mechanisms are integrated

Development of 3D anti-Swing control for hydraulic knuckle boom crane

In this paper, 3D anti-swing control for a hydraulic loader crane is presented. The difference between hydraulic and electric cranes are discussed to show the challenges associated with hydraulic actuation. The hanging load dynamics and relevant kinematics of the crane are derived to model the system and create the 3D anti-swing controller. The anti-swing controller generates a set of tool point velocities which are added to the electro-hydraulic motion controller via feedforward. A dynamic simulation model of the crane is made, and the control system is evaluated in simulations with a path controller in actuator space. Simulation results show significant reduction in the load swing angles during motion using the proposed anti-swing controller in addition to pressure feedback. Experiments are carried out to verify the performance of the anti-swing controller. Results show that the implemented pressure feedback is crucial for reaching stability, and with it the control system yields good suppression of the swing angles in practice.publishedVersio

Development of Motion Control Systems for Hydraulically Actuated Cranes with Hanging Loads

Automation has been used in industrial processes for several decades to increase efficiency and safety. Tasks that are either dull, dangerous, or dirty can often be performed by machines in a reliable manner. This may provide a reduced risk to human life, and will typically give a lower economic cost. Industrial robots are a prime example of this, and have seen extensive use in the automotive industry and manufacturing plants. While these machines have been employed in a wide variety of industries, heavy duty lifting and handling equipment such as hydraulic cranes have typically been manually operated. This provides an opportunity to investigate and develop control systems to push lifting equipment towards the same level of automation found in the aforementioned industries. The use of winches and hanging loads on cranes give a set of challenges not typically found on robots, which requires careful consideration of both the safety aspect and precision of the pendulum-like motion. Another difference from industrial robots is the type of actuation systems used. While robots use electric motors, the cranes discussed in this thesis use hydraulic cylinders. As such, the dynamics of the machines and the control system designmay differ significantly. In addition, hydraulic cranes may experience significant deflection when lifting heavy loads, arising from both structural flexibility and the compressibility of the hydraulic fluid. The work presented in this thesis focuses on motion control of hydraulically actuated cranes. Motion control is an important topic when developing automation systems, as moving from one position to another is a common requirement for automated lifting operations. A novel path controller operating in actuator space is developed, which takes advantage of the load-independent flow control valves typically found on hydraulically actuated cranes. By operating in actuator space the motion of each cylinder is inherently minimized. To counteract the pendulum-like motion of the hanging payload, a novel anti-swing controller is developed and experimentally verified. The anti-swing controller is able to suppress the motion from the hanging load to increase safety and precision. To tackle the challenges associated with the flexibility of the crane, a deflection compensator is developed and experimentally verified. The deflection compensator is able to counteract both the static deflection due to gravity and dynamic de ection due to motion. Further, the topic of adaptive feedforward control of pressure compensated cylinders has been investigated. A novel adaptive differential controller has been developed and experimentally verified, which adapts to system uncertainties in both directions of motion. Finally, the use of electro-hydrostatic actuators for motion control of cranes has been investigated using numerical time domain simulations. A novel concept is proposed and investigated using simulations.publishedVersio

Development and evaluation of a weighing system for forestry cranes based on artificial neural networks

Sowohl in der Hackschnitzel- als auch Rundholzlogistik fehlen oft wichtige Referenzmengen für den dispositiven Einsatz, welche zumeist mit unzureichend genauen Schätzwerten vervollständigt werden. Um die Informationsqualität über die bewegten Holzmengen zu verbessern, können optional Kranwaagen zwischen Teleskopauge und Greifer am Kran des Forwarders montiert werden. Dies beeinflusst jedoch die Krankinematik und Manövrierfähigkeit negativ, bei zeitgleich sinkender Maschinenproduktivität aufgrund einer zur Messung notwendigen Unterbrechung des Ladeprozesses. In diesem Beitrag wird eine datenbasierte Methode präsentiert, welche einen dynamischen Wiegeprozess im kontinuierlichen Ladevorgang bei modernen Forstkränen ermöglicht, ohne dass eine zusätzliche Hardware-Komponente auf der Maschine verbaut werden muss. Bei dieser Methode wird ein Ladezyklus automatisiert erkannt und die geladene Masse anhand eines künstlichen neuronalen Netzwerkes (KNN) abgeschätzt. Als Eingangsgrößen dienen Signale von Sensoren, die auf auf modernen Forwardern serienmäßig installiert sind. Für die Verarbeitung von zeitbasierten Sensordaten in einem neuronalen Netz hat sich die Long-Short-Term-Memory(LSTM)-Architektur bewährt. Basierend auf LSTM-Zellen wurde ein entsprechendes Netzwerk entworfen, trainiert und anschließend optimiert. Im Test zeigt sich für einen einzelnen Ladezyklus ein mittlerer Gesamtskalenfehler von 1,5 %, bezogen auf 1.000 kg. Für einen voll beladenen Forwarder resultiert dies in einem Gesamtmassenfehler kleiner 1,2 %.In both log and chip logistics, important reference data for logistic purposes are often lacking, as they are usually completed with insufficiently accurate estimates. In order to obtain higher quality information on the moving timber quantities, optional crane scales can be mounted between the telescope and the grapple of the forwarder. However, this has a negative effect on the crane kinematics and manoeuvrability while at the same time machine productivity is reduced due to an interruption in the loading process necessary for measurement. In this paper, a data-based method is presented which allows dynamic weighing in a continuous loading process for modern forestry cranes without the need to install an additional hardware component on the machine. This allows a cost-effective and comprehensive application. In the course of this method, a loading cycle is automatically detected, and the loaded mass is estimated by means of an artificial neural network (ANN). Signals from sensors installed as standard on modern forwarders serve as input variables. The Long Short-Term Memory (LSTM) architecture for the neural network has proven itself for handling these time-based sensor data. Based on LSTM cells, an appropriate network was designed, trained and subsequently optimized. The test shows an average full-scale error of 1.5% per 1,000 kg for a single loading cycle. For a fully loaded forwarder, this results in a total mass error of less than 1.2%

Top Quark Physics at the Tevatron

We review the field of top-quark physics with an emphasis on experimental techniques. The role of the top quark in the Standard Model of particle physics is summarized and the basic phenomenology of top-quark production and decay is introduced. We discuss how contributions from physics beyond the Standard Model could affect top-quark properties or event samples. The many measurements made at the Fermilab Tevatron, which test the Standard Model predictions or probe for direct evidence of new physics using the top-quark event samples, are reviewed here.Comment: 50 pages, 17 figures, 2 tables; version accepted by Review of Modern Physic

Design and control of a loader mechanism for the NMBU agricultural robot

Despite the development of new technologies, manual labour still continuous to play a large role within most modern agricultural operations, especially during harvest. Consequently, there is an increasing demand for new machines to reduce labour as a mean to limit costs, while increasing efficiency in a sustainable manner. This thesis concern itself with the design of a mechanism and control system for a robot arm that can substitute workers in logistical operations during strawberry harvest. More specifically, by lifting berry crates onto a robot platform and transporting them from the fields and to the packaging facilities. The robot arm is to be mounted on the platform composing a vehicle- manipulator system. As this thesis is connected to a general research project on agricultural robotics at the Norwegian University of Life Sciences, the chosen platform is the associated field robot Thorvald II. The thesis is divided into two parts, where Part I concerns the mechanical design of the robot arm, while Part II propose a system for controlling the mechanism. The design development process has involved assessments of available solutions before selecting components on the basis of controllability, mechanical properties and costs. The process of selection in Part II is however, based on finding solutions that are compatible with the robot platform’s network (Controller Area Network) and operating system (Robotic Operating System). Part I: Design and Mechanics The design of the robot arm presented in this thesis begun with a preliminary feasibility study conducted by Bjurbeck in September 2016. Following the assessment of this study, the robot arm is designed to have two degrees of freedom operating in the xz-plane. When mounted on the platform, the arm will be free to operate in a 3-dimensional space, as the platform moves in x and y-direction, and rotates around the z-axis. The arm is assembled from two parallel link pairs made from rectangular aluminium tubes, and a revolute and prismatic joint. Both joints are actuated by LinAk LA36 linear electric actuators. The end effector of the arm is a gripper head designed to grasp the handles of the strawberry crate. The gripper head is self-aligning with the crate’s orientation in order to reduce the precision of control needed to envelop and grasp the crate. The frame of the gripper head is made from aluminium angle profiles and sheet metal. A worm drive DC motor actuate the gripper claws via a double link mechanism. Part II: Modeling and Control The geometry of the design presented in Part I is modelled mathematically and the inverse kinematics solved analytically. The kinematics will be used in future implementation of a position control system. Two RoboteQ SDC2160 dual-channel controllers are chosen to control all four actuator mo- tors. The linear actuators are controlled in closed loop position tracking mode with absolute feedback. The gripper motor is controlled in open loop mode with end stop switches detecting the position of the claws. Experiments was conducted to match the controllers with the actuator motors. The experiments revealed firmware issues with the controller. The experiments also affirmed the controller need a script to operate the actuators efficiently. The thesis provides the foundations to build a prototype and write an operating script to test the mechanical design and control system.Til tross for den stadige utviklingen av ny teknologi spiller manuelt arbeid fortsatt en stor rolle i moderne landbruk, særlig i innhøsting. På grunn av den store arbeidkraften som trengs er det en stadig større etterspørsel etter nye maskiner som kan redusere behovet for manuelt arbeid for å redusere utgifter og effektivisere gårdsbruk på en bærekraftig måte. Denne masteroppgaven omhandler det mekaniske designet og reguleringssystemet til en robotarm laget for å kunne erstatte arbeidere i oppgaver tilknyttet logistikk ved innhøsting av jordbær. Dette gjøres ved at armen løfter kasser med bær opp på en robotplattform som transporterer kassene fra jordet og til et pakkeri. Robotarmen er da montert oppå plattformen. Siden oppgaven er tilknyttet et forskningsprosjekt i landbruksrobotikk ved Norges miljø- og biovitenskapelige universitet, var det naturlig å velge den universitetets robot Thorvald II som plattform.submittedVersionM-MP