Michael Rygaard Hansen

Comparison of Post Weld Treatment of High Strength Steel Welded Joints in Medium Cycle Fatigue

This paper presents a comparison of three post-weld treatments for fatigue life improvement of welded joints. The objective is to determine the most suitable post-weld treatment for implementation in mass production of certain crane components manufactured from very high-strength steel. The processes investigated are: burr grinding, TIG dressing and ultrasonic impact treatment. The focus of this investigation is on the so-called medium cycle area, i.e. 10 000–500 000 cycles and very high stress ranges. In this area of fatigue design, the use of very high-strength steel becomes necessary, since the stress range can exceed the yield-strength of ordinary structural steel, especially when considering positive stress ratios (R > 0). Fatigue experiments and qualitative evaluation of the different post-weld treatments leads to the selection of TIG dressing. The process of implementing TIG dressing in mass production and some inherent initial problems are discussed. The treatment of a few critical welds leads to a significant increase in fatigue performance of the entire structure and the possibility for better utilization of very high-strength steel.

Modelling of a special class of spherical parallel manipulators with euler parameters

A method of workspace modelling for spherical parallel manipulators (SPMs) of symmetrical architecture is developed by virtue of Euler parameters in the paper. The adoption of Euler parameters in the expression of spatial rotations of SPMs helps not only to eliminate the possible singularity in the rotation matrix, but also to formulate all equations in polynomials, which are more easily manipulated. Moreover, a homogeneous workspace can be obtained with Euler parameters for the SPMs, which facilitates the evaluation of dexterity. In this work, the problem of workspace modelling and analysis is formulated in terms of Euler parameters. An equation dealing with boundary surfaces is derived and branches of boundary surface are identified. Evaluation of dexterity is explored to quantitatively describe the capability of a manipulator to attain orientations. The singularity identification is also addressed. Examples are included to demonstrate the application of the proposed method.

A general method for analysis of planar mechanisms using a modular approach

A method that covers both kinematic, inverse dynamic, dynamic, and static analysis of any type of planar mechanism is presented. The method is based on a subdivision of the mechanism to be analyzed into kinematic chains that are categorized as either neutral or expansion modules. The neutral modules are the well known Assur Groups, characterized by the fact that they have no effect on the degree of freedom of the mechanism. On the contrary each expansion module increases the degree of freedom by one. The coordinates that correspond to the indeterminancy of the expansion modules may be identified as a set of independent coordinates for the subdivided mechanism and used in any type of analysis. The method as it is described in the present paper has been implemented in a menu-controlled PC computer program CADME. A number of practical observations concerning the implementation of a modular approach is made and discussed.

Integrated dimensional and drive-train design optimization of a light-weight anthropomorphic arm

An approach to minimize the mass of robotic manipulators is developed by integrated dimensional and drive-train optimization. The method addresses the influences of dimensions and characteristics of drive-trains in the design optimization. Constraints are formulated on the basis of kinematic performance and dynamic requirements, whereas the main objective is to minimize the total mass. Case studies are included to demonstrate the application of the optimization method in the design of assistive robots.

A multi level approach to synthesis of planar mechanisms

A multi level approach to synthesis of planar mechanisms is presented. The approach covers both structural and dimensional synthesis of planar rigid body mechanisms containing revolute and translational joints. The synthesis is based on four different criteria. Firstly the type of mechanism is chosen with a view to get the simplest mechanism that satisfactorily fulfills the remaining three criteria. Two of these criteria are formulated as constraints on the kinematic behavior and the total area occupied by the mechanism, respectively. The fourth criteria is simply the desired minimization of the reactive forces/moments that appear in the mechanism. The desired kinematic behavior is based on a finite number, typically 1, ..., 6, of points in time (positions of the mechanism) where the position and orientation of up to two output bodies may be prescribed. The constraints on occupied areas are labelled territory constraints and formulated as a number of restricted areas (boxes). A synthesis is automatically performed at five levels. At the first level the structure of the mechanism is decided. At the second level initial dimensions for the given type of mechanism are found by random checking. At the third level the constraints on the kinematic behavior is fulfilled. At the fourth level the territory constraints are taken into account and, finally, at the fifth level the minimization of reactions is carried out. The entire approach has been implemented in a software package SYNMEC that runs on PCs and constitutes a way of performing the synthesis of a mechanism that is general and flexible with respect to both the type of mechanism that may be synthesized as well as the desired behavior upon which the synthesis is based.

Forward kinematics of spherical parallel manipulators with revolute joints

The paper deals with the forward kinematics of spherical parallel manipulators (SPMs). A polynomial solution of forward kinematics is presented with a novel approach of utilizing the input-output (I/O) equations of spherical four-bar linkages. In this method, the closed-loop kinematic chain of an SPM is separated into two four-bar spherical chains, for which the input-output equations can be obtained. Based on the input-output equations of spherical four-bar linkage, an eighth-order polynomial equation of joint angles is obtained, which yields the orientation of the end-effector of an SPM in terms of the unit vectors for joint axes. Examples are included to demonstrate the application of the developed method.

An Efficient Method for Synthesis of Planar Multibody Systems Including Shape of Bodies as Design Variables

A point contact joint has been developed and implemented in a joint coordinate based planar multibody dynamics analysis program that also supports revolute and translational joints. Further, a segment library for the definition of the contours of the point contact joints has been integrated in the code and as a result any desired contour shape may be defined. The sensitivities of the basic physical variables of a multibody system, i.e., the positions, velocities, accelerations and reactions of the system with respect to the automatically identified independent design variables may be determined analytically, allowing design problems where the shape of the bodies are of interest to be handled in both a general and efficient way.

Numerical modeling of sandwich panel response to ballistic loading - energy balance for varying impactor geometries

A sandwich panel is described by an axisymmetric lumped mass— spring model. The panel compliance is simplified, considering only core shear deformation uniformly distributed across the core thickness. Transverse penetrating impact is modeled for impactors of diameters comparable to the panel thickness but significantly smaller than panel length dimensions. Experimental data for the total loss in impactor kinetic energy and momentum and estimated damage energy are described. For a selection of impactor tip shapes, the numerical model is used to evaluate different simplified force histories between the impactor and the panel during penetration. The force histories are selected from a primary criterion of conservation of linear momentum in the impactor—panel system, and evaluated according to agreement with the total measured energy balance.

Model Based Design Optimization of Operational Reliability in Offshore Boom Cranes

Abstract This paper presents a model based approach for design of reliable electro-hydraulic motion control systems for offshore material handling cranes. The approach targets the system engineer and is based on steady-state computations, dynamic time domain simulation and numerical optimization. In general, the modelling takes into account the limited access to component data normally encountered by engineers working with system design. A system model is presented which includes the most important characteristics of both mechanical system and hydraulic components such as the directional control valve and the counterbalance valve. The model is used to optimize the performance of an initial design by minimizing oscillations, maximizing the load range and maintaining operational reliability.

Robust adaptive backstepping control design for a Nonlinear Hydraulic-Mechanical System

The complex dynamics that characterize hydraulic systems make it difficult for the control design to achieve prescribed goals in an efficient manner. In this paper, we present the design and analysis of a robust nonlinear controller for a Nonlinear Hydraulic-Mechanical (NHM) System. The system consists of an electrohydraulic servo valve and two hydraulic cylinders. Specifically, by considering a part of the dynamics of the NHM system as a norm-bounded uncertainty, two adaptive controllers are developed based on the backstepping technique that ensure the tracking error signals asymptotically converge to zero despite the uncertainties in the system according to the Barbalat lemma. The resulting controllers are able to take into account the interval uncertainties in Coulomb friction parameters and in the internal leakage parameters in the cylinders. Two adaptation laws are obtained by using the Lyapunov functional method and inequality techniques. Simulation results demonstrate the performance and feasibility of the proposed method.