Sliding Mode Analysis of a Counterbalance Valve Induced Instability in an Electrohydraulic Drive

This paper analyzes dynamic effects of an electro-hydraulic drive which uses a counter-balance valve for rod volume compensation. It shows that local stability analysis is not sufficient in this particular case to get general statements of the system's chattering properties. A reduced-order switched system is proposed to gain deeper insights in system dynamics with saturation effects such as the end-stop of a valve poppet and solutions are compared numerically to the full-system dynamics which incorporates pressure built-up, piston and valve dynamics as well as motor dynamics. It is shown that in cases of e.g. fast valves with small cracking pressures undesirable chattering of the full system exists which can be easily understood in terms of the reduced-order system in form of sliding mode solutions. The paper also describes under which conditions such sliding modes exist, how they behave and how they can be interpreted in terms of the full system.

Novel Methods and Technologies for Assessing Usability of Off-Road Machines in R&D Phase - The Lutergo Laboratory

A novel intelligent experimental research environment (LUTERGO laboratory) for developing the usability of off-road machines was created at LUT University. The environment combines a real-time simulator and an experimental system for measuring human body responses when driving the virtual prototypes of machines. Based on the quantities measured from the operator, such as heart rate, electrodermal, muscular, and brain activity, the stress level of the operator can be evaluated. It is assumed that by combining simulated machine data and biosignals, the usability of every virtual prototype of a new machine can be assessed during the R&D process. This is an alternative to a traditional approach when usability is studied with physical prototypes after conceptual R&D phases using qualitative data from questionnaires. The paper describes the structure and capabilities of the LUTERGO laboratory. Results of the initial tests are presented, which studied the influence of hydraulic valve dynamics on excavator vibration and operator biosignals. The results show that the biosignal parameters used as stress indicators change following the variation of time constant for directional valves controlling the main boom cylinders of the excavator. The paper concludes with future research directions using the novel environment.

Effect of the Location of Strut Chordae Insertion on Computational Modeling and Biomechanical Evaluation of Mitral Valve Dynamics

The strut chordae (SC) have a unique structure and play an important role in reinforcing the tunnel-shaped configuration of the mitral valve (MV) at the inflow and outflow tracts. We investigated the effect of varying the SC insertion location on normal MV function and dynamics to better understand the complex MV structures. A virtual parametric MV model was designed to replicate a normal human MV, and a total of nine MV modes were created from combinations of apical and lateral displacements of the SC insertion location. MV function throughout the full cardiac cycle was simulated using dynamic finite element analysis for all MV models. While the leaflet stress distribution and coaptation showed similar patterns in all nine MV models, the maximum leaflet stress values increased in proportion to the width of the SC insertion locations. A narrower SC insertion location resulted in a longer coaptation length and a smaller anterior coaptation angle. The top-narrow MV model demonstrated the shortest anterior leaflet bulging distance, lower stresses across the anterior leaflet, and the lowest maximum stresses. This biomechanical evaluation strategy can help us better understand the effect of the SC insertion locations on mechanism, function, and pathophysiology of the MV.