Fe Frans Veldpaus

Rigid body motion calculated from spatial co-ordinates of markers

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A least-squares algorithm for the equiform transformation from spatial marker co-ordinates

The present paper describes an algorithm for estimating the translation vector and the rotation matrix of a moving body from noisy measurements on the spatial co-ordinates of at least three non-collinear markers. A sensitivity analysis of the estimated parameters and of the helical axis is presented in terms of characteristics of the marker distribution. The implementation of the proposed algorithm in a FORTRAN-subroutine is appended.

A three-dimensional mathematical model of the knee-joint

Abstract A three-dimensional analytical model of the knee-joint is presented, taking into account the geometry of the joint surfaces as well as the geometry and material properties of the ligaments and capsule. The position of a large number of points on the joint surfaces is measured and the geometry of these surfaces is then approximated by polynomials in space. The ligaments and capsule are represented by a number of non-linear springs, with material properties selected from the literature. For a given three-dimensional loading (forces as well as moments) at various flexion-extension angles, the location of contact points, magnitude and direction of contact forces, magnitude of ligament elongation and ligament forces can be calculated. In the results presented in this paper special attention is given to the anterior-posterior laxity of a joint. A sensitivity study was undertaken to evaluate the model response due to some of the model parameters and to gain a better understanding of the function of the elements in the model. It is concluded that the predictions of the model agree well with experiments described in the literature.

The mechanical properties of porcine aortic valve tissues

In uniaxial tensile experiments in vitro mechanical properties of the different parts of porcine aortic valves, i.e. the leaflets, the sinus wall and the aortic wall, have been dealt with. Tissue strips cut in different directions were investigated. The collagen bundles in the leaflets show a stiffening effect and cause a marked anisotropy: within the physiological range of strains the largest slopes of the stress-strain curves of leaflet specimens in the bundle direction are a factor of about 20 larger than those of specimens taken along the perpendicular direction. For the sinus and aortic tissues, these values are 50-200 times smaller than those obtained from the leaflet specimens in the bundle direction. Two aspects of viscoelastic behaviour were examined: the strain rate sensitivity of the stress-strain curves and the relaxation behaviour. The stress-strain curves of the different valve parts appeared to be rather insensitive to the strain rate: the most pronounced sensitivity observed in our experiments, was a doubling of the stress at the same strain caused by a hundredfold increase of the strain rate. In analyzing the relaxation behaviour, use was made of the relaxation model proposed by Fung (1972, in Biomechanics, its Foundations and Objectives; Fung, Perrone and Anliker. Prentice Hall). In the leaflets, about 45% stress relaxation was found whereas this amounted to 30% in the sinus and aortic walls. Predictions based upon the model indicate that on cyclic loading the larger viscous losses have to be expected in the leaflets.

Aortic valve histology and its relation with mechanics—Preliminary report

Histological secitons of relaxed porcine aortic valves were studied from a mechanical point of view. The observations are combined into a tractable scheme of the tissue structure of the aortic valve. The valve leaflets can be regarded as an elastic meshwork, reinforced with stiff collagen bundles, showing an arrangement in one particular direction. The sinus walls consist of smooth muscle tissue, embedded in an elastic meshwork. The line of attachment of the leaflets to the sinus walls is constituted by the aortic ring, a crownlike fibrocartilaginous structure, containing large amounts of collagen fibres. This simple scheme of the tissue structure can be expected to provide important starting-points for both the interpretation of experimental results and the theoretical modelling of aortic valve mechanics and kinematics.

Simulation of forming processes, using the arbitrary Eulerian Lagrangian formulation

The finite element method is frequently used to simulate forming processes for the purpose of predicting the quality of the final product and the load on the tool. If the method is based on either the Eulerian or the Lagrangian formulation, some simulations are arduous or even impossible. To avoid this the arbitrary Eulerian-Lagrangian (AEL) formulation can be used. In this paper the theoretical background of this formulation is presented and some new concepts are introduced. The formulation offers the possibility to improve the geometry of distorted elements. A procedure for automatic mesh adaptation is described. The formulation is employed in the simulation of some axisymmetric forming processes.

Analysis and control of a flywheel hybrid vehicular powertrain

Vehicular powertrains with an internal combustion engine, an electronic throttle valve, and a continuously variable transmission (CVT) offer much freedom in controlling the engine speed and torque. This can be used to improve fuel economy by operating the engine in fuel-optimal operating points. The main drawbacks of this approach are the low driveability and, possibly, an inverse response of the vehicle acceleration after a kick-down of the drive pedal. This paper analyzes a concept for a novel powertrain with an additional flywheel. The flywheel plays a part only in transient situations by (partly) compensating the engine inertia, making it possible to optimize fuel economy in stationary situations without loosing driveability in transients. Two control strategies are discussed. The first one focuses on the engine and combines feedback linearization with proportional control of the CVT ratio. The CVT controller has to be combined with an engine torque controller. Three possibilities for this controller are discussed. In the second strategy, focusing on control of the vehicle speed, a bifurcation occurs whenever a downshift of the CVT to the minimum ratio is demanded. Some methods to overcome this problem are introduced. All controllers are designed, using a simple model of the powertrain. They have been evaluated by simulations with an advanced model.

An Optimal Continuous Time Control Strategy for Active Suspensions with Preview

Abstract A continuous time control strategy for an active suspension with preview, based on optimal control theory, is presented. No approximation is needed to model the time delay between the excitation of the front and the rear wheels. The suspension is applied to a two DOF model of the rear side of the tractor of a tractor-semitrailer. The purpose of the suspension is to reduce either the required suspension working space or the maximum absolute acceleration of the sprung mass, without an increase of the dynamic tire force variation. For a step function as road input, reductions of 65% and 55%, respectively, are possible compared with a passive suspension.

Control of a hydraulically actuated continuously variable transmission

Vehicular drivelines with hierarchical powertrain control require good component controller tracking, enabling the main controller to reach the desired goals. This paper focuses on the development of a transmission ratio controller for a hydraulically actuated metal push-belt continuously variable transmission (CVT), using models for the mechanical and the hydraulic part of the CVT. The controller consists of an anti-windup PID feedback part with linearizing weighting and a setpoint feedforward. Physical constraints on the system, especially with respect to the hydraulic pressures, are accounted for using a feedforward part to eliminate their undesired effects on the ratio. The total ratio controller guarantees that one clamping pressure setpoint is minimal, avoiding belt slip, while the other is raised above the minimum level to enable shifting. This approach has potential for improving the efficiency of the CVT, compared to non-model based ratio controllers. Vehicle experiments show that adequate tracking is obtained together with good robustness against actuator saturation. The largest deviations from the ratio setpoint are caused by actuator pressure saturation. It is further revealed that all feedforward and compensator terms in the controller have a beneficial effect on minimizing the tracking error.

Application of computed phase transformation power to control shape memory alloy actuators

This paper presents a control law for shape memory alloy (SMA) wire actuators. Unlike most laws reported in the literature, this control law includes both a feedback and an open-loop part. The open-loop part takes into account the stress - strain - temperature behaviour of SMA wires, as well as the dynamics of the heating and cooling process. A constitutive model for a NiTi wire is developed. This model is a compromise between accurate description of the real behaviour, and simplicity, since it must be used on-line for the determination of the open-loop part of the control law. The method is tested both in simulations and experiments on a system with one degree of freedom. The tracking performance of the controlled system was investigated for a number of trajectory-following tasks. The tracking error obtained with the proposed control method is considerably smaller than with feedback control only.