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

Adaptive Feedforward Control of a Pressure Compensated Differential Cylinder

This paper presents the design, simulation and experimental verification of adaptive feedforward motion control for a hydraulic differential cylinder. The proposed solution is implemented on a hydraulic loader crane. Based on common adaptation methods, a typical electro-hydraulic motion control system has been extended with a novel adaptive feedforward controller that has two separate feedforward states, i.e, one for each direction of motion. Simulations show convergence of the feedforward states, as well as 23% reduction in root mean square (RMS) cylinder position error compared to a fixed gain feedforward controller. The experiments show an even more pronounced advantage of the proposed controller, with an 80% reduction in RMS cylinder position error, and that the separate feedforward states are able to adapt to model uncertainties in both directions of motion.publishedVersio

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

Advanced Control Strategies for Mobile Hydraulic Applications

Mobile hydraulic machines are affected by numerous undesired dynamics, mainly discontinuous motion and vibrations. Over the years, many methods have been developed to limit the extent of those undesired dynamics and improve controllability and safety of operation of the machine. However, in most of the cases, today\u27s methods do not significantly differ from those developed in a time when electronic controllers were slower and less reliable than they are today. This dissertation addresses this aspect and presents a unique control method designed to be applicable to all mobile hydraulic machines controlled by proportional directional valves. In particular, the proposed control method is targeted to hydraulic machines such as those used in the field including construction (wheel loaders, excavators, and backhoes, etc.), load handling (cranes, reach-stackers, and aerial lift, etc.), agriculture (harvesters, etc.), forestry, and aerospace. For these applications the proposed control method is designed to achieve the following goals: A. Improvement of the machine dynamics by reducing mechanical vibrations of mechanical arms, load, as well as operator seat; B. Reduction of the energy dissipation introduced by current vibration damping methods; C. Reduction of system slowdowns introduced by current vibration damping methods. Goal A is generally intended for all machines; goal B refers to those applications in which the damping is introduced by means of energy losses on the main hydraulic transmission line; goal C is related to those applications in which the vibration attenuation is introduced by slowing down the main transmission line dynamics. Two case studies are discussed in this work: 1. Hydraulic crane: the focus is on the vibrations of the mechanical arms and load (goals A and B). 2. Wheel loader: the focus is on the vibrations of the driver\u27s seat and bucket (goals A and C). The controller structure is basically unvaried for different machines. However, what differs in each application are the controller parameters, whose adaptation and tuning method represent the main innovations of this work. The proposed controller structure is organized so that the control parameters are adapted with respect to the instantaneous operating point which is identified by means of feedback sensors. The Gain Scheduling technique is used to implement the controller whose set of parameters are function of the specific identified operating point. The optimal set of control parameters for each operating point is determined through the non-model-based controller tuning. The technique determines the optimal set of controller parameters through the optimization of the experimental machine dynamics. The optimization is based on an innovative application of the Extremum Seeking algorithm. The optimal controller parameters are then indexed into the Gain Scheduler. The proposed method does not require the modification of the standard valve controlled machine layout since it only needs for the addition of feedback sensors. The feedback signals are used by the control unit to modify the electric currents to the proportional directional valves and cancel the undesired dynamics of the machine by controlling the actuator motion. In order for the proposed method to be effective, the proportional valve bandwidth must be significantly higher than the frequency of the undesired dynamics. This condition, which is typically true for heavy machineries, is further investigated in the research. The research mostly focuses on the use of pressure feedback. In fact, although the use of position, velocity, or acceleration sensors on the vibrating bodies of the machine would provide a more straightforward measurement of the vibration, they are extremely rare on mobile hydraulic machines where mechanical and environmental stress harm their integrity. A comparison between pressure feedback and acceleration feedback alternatives of the proposed method is investigated with the aim to outline the conditions making one alternative preferable over the other one (for those applications were both alternatives are technically viable in terms of sensors and wiring reliability). A mid-sized hydraulic crane (case study 1) was instrumented at Maha Fluid Power Research Center to study the effectiveness of the proposed control method, its stability and its experimental validation. Up to 30% vibration damping and 40% energy savings were observed for a specific cycle over the standard vibration damping method for this application. The proposed control method was also applied to a wheel loader (case study 2), and up to 70% vibrations attenuation on the bucket and 30% on the driver\u27s cab were found in simulations. These results also served to demonstrate the applicability of the control method to different hydraulic machines. Improved system response and a straightforward controller parameters tuning methodology are the features which give to the proposed method the potential to become a widespread technology for fluid power machines. The proposed method also has potential for improving several current vibration damping methods in terms of energy efficiency as well as simplification of both the hydraulic system layout and tuning process

Offshore Wind Turbine Access Using Knuckle Boom Cranes

Doktorgradsavhandling, Fakultet for teknologi og realfag, Institutt for ingeniørvitenskap, 2016There is a great need for renewable and sustainable energy today and there are several different sources for this energy where offshore wind is one that has a great estimated planned power production. Wind power production has for many years been produced onshore, but installing the wind turbines offshore has some benefits due to higher and more stable wind conditions. The majority of installed wind turbines are today bottom fixed, but when moving to deeper waters it is too high cost in building and installing foundation, which brings the possibility of using floating wind turbines. There are, however, also challenges due to the access for both the fixed and floating offshore wind turbines. During startup, repair or maintenance there is a demand for easy access of both personnel and equipment. This dissertation mainly deals with offshore access solutions systems or parts of those systems. The access solutions are systems that transfers personnel or equipment from a floating vessel to a fixed or floating offshore structure. Work done using a small scale hydraulic manipulator is described in Papers A and B, where paper A deals with the kinematic motion control of such a small scale redundant manipulator mounted on a moving Stewart platform, imitating the motion of a floating vessel. The manipulator tries to keep the tool point at a fixed reference point by the use of the pseudo-inverse Jacobian. Used in the experimental verification is a high precision laser tracker which measures the position of the tool point. Paper B uses the same manipulator and has in addition a hanging payload attached to the tool point. A LQR control strategy is used to minimize the vibration of the hanging payload when the manipulator moves the tool point relative to a ground fixed coordinate system. Paper C is concerned with the inherent oscillatory nature of pressure compensated motion control of a hydraulic cylinder subjected to a negative load and suspended by means of a counter-balance valve. The method proposed in this paper has the focus on pressure feedback and is compared to classical control strategies. In paper D input shaping is used for the slewing motion control of a full scale mobile crane. The flexibility of the crane causes vibrations when slewing and by knowing the natural frequency and damping, the command signal is shaped so there are no residual vibrations. Experimental verification is carried out by means of a laser tracker. Finally, the work done in Paper E deals with active heave compensation from a fixed structure to a floating vessel. Modeling of the hydraulic winch is done and a frequency response function is obtained. The active heave compensation was experimentally verified using the full scale mobile crane as the fixed structure with a winch mounted on it and the Stewart platform as the moving structure. Both results from active heave compensation and constant tension are presented. The payload in the experiments is a 400kg steel structure

Modelling and control of mechatronic and robotic systems

3noopenopenGasparetto A.; Seriani S.; Scalera L.Gasparetto, A.; Seriani, S.; Scalera, L

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

This paper presents a self-contained pump-controlled hydraulic linear drive including an innovative load holding sub-circuit. For safety critical applications such as crane manipulators, locking valves or load holding valves are enforced by legislation, but the load holding functionality may also be used actively to decrease the energy consumption for applications where the load is kept stationary for longer periods of time. The system proposed in this paper is based on a simple hydraulic architecture using two variable-speed electric motors each connected to a fixed-displacement pump. This architecture is well-known in academic literature, but in this paper a novel load holding sub-circuit has been included. To control this load holding functionality, the low chamber pressure needs to be controlled accurately, while still being able to control the motion of the cylinder piston as well. Due to strong cross-couplings between cylinder piston motion and chamber pressures this task is non-trivial. The control for opening the locking valves is indirect in the sense that it is controlled via the chamber pressures, which are actively controlled. The fundamental control strategy presented in this paper is based on transforming the highly coupled physical states to virtual states, significantly reducing cross-couplings.publishedVersio

Lunar surface construction and assembly equipment study: Lunar Base Systems Study (LBSS) task 5.3

A set of construction and assembly tasks required on the lunar surface was developed, different concepts for equipment applicable to the tasks determined, and leading candidate systems identified for future conceptual design. Data on surface construction and assembly equipment systems are necessary to facilitate an integrated review of a complete lunar scenario

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