This has led to the development of a novel, patent pending, concept that significantly reduces the described oscillations.
Jesper Kirk Sørensen
Når gods flyttes fra båt til rigg til havs, vil pakken som blir løftet bli utsatt for farlige svingninger. I doktorgradsavhandlingen analyserer Jesper Kirk Sørensen hva som skjer, og foreslår løsninger for å motvirke svingningene. Løsningene er så gode at det er søkt patentrettigheter på dem.
Jesper Kirk Sørensen disputerer på Fakultet for teknologi og realfags doktorgradsprogram med spesialisering i mekatronikk.
Imagine you want to lift a heavy burden from a truck onto the ground, or perhaps from one ship to another. This lift would often be carried out by a hydraulic knuckle boom crane: a crane type normally consisting of two arms that are moved by hydraulic cylinders to control the tip of the crane.
Now imagine the crane oscillating uncontrollable when it is moving with the same heavy burden. This is of course a safety concern, but also it reduces the productivity and stresses the mechanical construction of the crane so it will wear down quicker.
To investigate ways to reduce these oscillations has been the main topic of Jesper Kirk Sørensen’s recently published dissertation “Reduction of Oscillations in Hydraulically Actuated Knuckle Boom Cranes”.
By law it is required that load-carrying applications, like these cranes, should contain a device able to keep both the crane and the load on its hook lifted in case of the failure. The most commonly used of these devices is a hydraulic valve called a counterbalance valve.
To decide the direction and speed of the hydraulic cylinders are often used a so-called pressure compensated directional proportional valve. This valve has some useful properties like sharing of the oil flow so more than one cylinder can be ran at the same time and making the inlet oil flow (hence the speed of the cylinder) independent of how much load is being lifted.
However, the combination of these two valve types tends to create the oscillations as mentioned. Unfortunately, there is no general solution to the problem that solves it in all situations.
The effort was mainly split in two:
First, was looked into existing solutions with the focus on the ones not requiring computer based control systems to function. This was done with reliability and robustness in mind. The investigated identified that the use of a pressure control valve instead of the pressure compensated directional proportional valve is a good commercially available solution to deal with the problematic oscillations. However, one drawback of the valve is that it does not have the load independency function. In the dissertation is proposed a control strategy to handle this issue.
In the second part of the perspective of the search was broadened to include solutions using control solutions. This has led to the development of a novel, patent pending, concept that significantly reduces the described oscillations. The idea, in short, is to manipulate the pressure compensator of the directional proportional valve, in a way so that the previous mentioned useful properties (flow sharing and load independency) are maintained, just without oscillating nature of the system.
Kandidaten: Jesper Kirk Sørensen graduated in 2010 from Aalborg University, Denmark, with a MSc in Electric Mechanical System Design. He worked two years in the Wind Turbine industry, before beginning as a PhD candidate in the Mechatronics group at University of Agder in 2012. A position being held until 2016. Currently he is employed at R&D (Hinnerup, Denmark), mainly working with the design of heavy duty test systems.
Prøveforelesning og disputas finner sted i Rom C2-042, Campus Grimstad.
Visedekan for forskning, Andreas Prinz, leder disputasen.
Tid for prøveforelesning: Tirsdag 13. desember 2016 kl 10:00
Oppgitt emne for prøveforelesning: "The flow forces in hydraulic valves - physical explanation, mathematical modelling and consequences to spool position control"
Tid for disputas:Tirsdag 13. desember 2016 kl 12:00
Tittel på avhandling: «Reduction of Oscillations in Hydraulic Actuated Knuckle Boom Cranes»
Søk etter avhandlingen i AURA - Agder University Research Archive, som er et digitalt arkiv for vitenskapelige artikler, avhandlinger og masteroppgaver fra ansatte og studenter ved Universitetet i Agder. AURA blir jevnlig oppdatert.
Førsteopponent: Professor Bernhard Manhartsgruber, Johannes Kepler Universitet, Austria
Annenopponent:Førsteamanuensis Niels Leergaard Pedersen, Danmarks Tekniske Universitet
Bedømmelseskomitéen er ledet av professor Joao Leal, UiA