Andres Kecskemethy | University of Duisburg-Essen (original) (raw)

Papers by Andres Kecskemethy

Advances in Robot Kinematics 2016, 2017

The accurate reproduction of bone motion during normal gait using noninvasive external sensors is... more The accurate reproduction of bone motion during normal gait using noninvasive external sensors is still an open issue: Using skin markers may lead to large artifacts due to skin sliding, while using newer technologies such as fluoroscopy allows only for short exposure in small regions due to radiation limits, and bone pins used in the past are today prohibited due to the risk of inflammations and pain. This paper presents a simple method for noninvasive bone motion estimation based on palpating prominent bone landmarks via tracked pressure foil planes, where three such landmarks suffice for bone pose estimation. Its mathematical formulation corresponds to determining the pose of a rigid body carrying three ellipsoids when the "pressure points", i.e. the perpendicular feet of the extremal distance points of the ellipsoids on the three pressure foil planes are given. In a previous paper, we showed that the planar case is akin to the 3PPR manipulator, but yielding instead of two solutions up to 64 complex and (up to now found) 48 real solutions. In this paper we treat the 3D case, which is solved numerically, and validate the concept by experimental measurements. It is shown that the method is numerically stable, yielding an accuracy of 0.8 • for flexion/extension and 1.2 • for abduction/adduction motion of the lower leg.

In this paper, impact effects between cylinder end faces are investigated based on a detailed ana... more In this paper, impact effects between cylinder end faces are investigated based on a detailed analysis of the geometric relationships for the different contact situations edge-edge, edge-face, and face-face. The corresponding impact effects are regarded by replacing the (rigid) contact point by a spring with line of action collinear to the main direction of penetration. An empirical blending formulae for providing smooth transition from one contact situation to the other, e.g., from point contact to flat contact, is presented. As an application example, the developed formulas are applied to the modeling and simulation of the inter-vertebral motion of the C5-C6 human cervical spine vertebrae pair, using cylinder-cylinder pairs to represent the facet joints. The application shows good agreement with experimental data, yielding an efficiency boost by a factor of 350 compared to the hyper-ellipsoid approach used in the commercial program MADYMO.

The article presents an object-oriented framework for representing guided spatial motion in multi... more The article presents an object-oriented framework for representing guided spatial motion in multibody systems. In this setting, the spatial track is regarded as a kinetostatic transmission element transmitting motion and forces as in a generic joint. For vector decompositions along the path, three different parametrizations (Frenet and Darboux frames, respectively, as well as the ODE generation proposed by Bishop) are analyzed. It is shown that for the Frenet frame parametrization, it is possible to avoid singularities at the points of inflection by a special blending technique. Track geometry is globally smoothed up to fifth order using B-Splines and Dierckx optimization routines, thus allowing for non-jerky acceleration layout. Roll-angle or banking information is additionally generated by globally smooth splines, thus also allowing for non-jerky rotations along the track. Local editing is made possible through the use of exponential blending functions. The result is a robust and ...

The gait of 47 stroke patients was measured using motion capture (MoCap) technology. 261 kinemati... more The gait of 47 stroke patients was measured using motion capture (MoCap) technology. 261 kinematical parameters (called “features”) were identified and extracted from each measurement. Stepwise linear regression was used to select and weight the features in order to numerically reproduce the functional scores provided by five medical experts. The numerical score accuracy corresponds to the reliability of the medical experts to determine the individual criteria.

This paper describes a new method for robot hand wrist singularity avoidance by using a virtual r... more This paper describes a new method for robot hand wrist singularity avoidance by using a virtual redundant axis. The method is described for the application of large spatial robot base motion compensation for a 6 degrees of freedom serial manipulator using an inertial measurement unit such that the end effector maintains a prescribed target location. The overall system is tested for a KUKA KR500 system and computer-generated as well as real wave signals with large amplitudes.

Numerical integration of dynamical equations of mechanical systems with impacts still poses many ... more Numerical integration of dynamical equations of mechanical systems with impacts still poses many open problems. On the one hand there exist powerful integration codes with embedded root finding capabilities. However, for these codes, the issues of (1) efficiency, (2) reliability and (3) stability of time progression through events still are not solved satisfactorily. In this paper, we present the implementation

Microprocessors and Microsystems, 1998

In this paper we present an integrated approach for very fast kinematic computations in multibody... more In this paper we present an integrated approach for very fast kinematic computations in multibody systems with complex structure. The approach relies on using optimized algorithms for generation of symbolic equations for kinematics together with application-specific hardware for their computation. The kinematic equations are optimized by incorporating closed-form solutions wherever possible. For optimized hardware, a computer board has been developed,

Computer-Aided Analysis of Rigid and Flexible Mechanical Systems, 1994

Discussed in this contribution is a particular approach for tackling the problem of formulating t... more Discussed in this contribution is a particular approach for tackling the problem of formulating the equations of motion of minimal order for complex mechanical systems. The obective is to arrive at a system of pure differential equations, which is robust and for which efficient integration techniques exist. This is achieved by a special treatment of the kinematics, which are formulated

at - Automatisierungstechnik, 1995

Mechanism and Machine Theory, 2015

ABSTRACT Structural synthesis is one of the most important tasks in the creative design of mechan... more ABSTRACT Structural synthesis is one of the most important tasks in the creative design of mechanisms. In the past decades, spatial parallel mechanisms have been extensively synthesized. However, structural synthesis of more complex spatial mechanisms with coupling chains is seldom addressed. This paper aims to propose a general method for synthesizing a class of important spatial mechanisms with coupling chains, called two-layer and two-loop (TLTL) mechanisms, which are the basic units for constructing multi-layer and multi-loop mechanisms with more complex couplings. First, the motion screw equation of TLTL mechanisms is derived, with which mobility or degree-of-freedom (DOF) of the class of mechanisms can be analyzed and rigid substructures can be detected. Then, a general method for structural synthesis of TLTL mechanisms is proposed on the basis of the principle of mobility analysis. Finally, TLTL mechanisms with fourteen kinds of degrees of freedom are synthesized, illustrating the effectiveness of the method.

Multibody System Dynamics, 2015

Musculoskeletal simulation has become an essential tool for understanding human locomotion and mo... more Musculoskeletal simulation has become an essential tool for understanding human locomotion and movement disorders. Muscle-actuated simulations require methods that continuously compute musculotendon paths, their lengths, and their rates of length change to determine muscle forces, moment arms, and the resulting body and joint loads. Musculotendon paths are often modeled as locally length minimizing curves that wrap frictionlessly over moving obstacle surfaces representing bone and tissue. Biologically accurate wrapping surfaces are complex, and a single muscle path may wrap around many obstacles. However, state-of-the-art muscle wrapping methods are either limited to analytical results for a pair of simple surfaces, or they are computationally expensive. In this paper, we introduce the Natural Geodesic Variation (NGV) method for the fast and accurate computation of a musculotendon's shortest path across an arbitrary number of general smooth wrapping surfaces, and an explicit formula for the path's exact rate of length change. The total path is regarded as a concatenation of straight-line segments between local surface geodesics, where each geodesic is naturally parameterized by its starting point, direction, and length. A. Scholz et al. The shortest path is computed by finding the root of a global path-error constraint equation that enforces that the geodesics connect collinearly with adjacent straight-line segments. High computational speed is achieved using Newton's method to zero the path error, with an explicit, banded Jacobian that maps natural variations of the geodesic parameters to patherror variations. Three simulation benchmarks demonstrate that the NGV method computes high-precision solutions for path length and rate of length change, allows for wrapping over biologically accurate surfaces, and is capable of simulating muscle paths over hundreds of surfaces in real time. We thus believe the NGV method will facilitate the development of more accurate yet very efficient musculoskeletal models.

PAMM, 2009

The present paper describes an approach for the reconstruction of the motion of the human spine b... more The present paper describes an approach for the reconstruction of the motion of the human spine based on marker tracking. The approach uses a spline curve of fifth degree to reproduce the contour of the central marrow line and a set of virtual sliders along the spline with fixed offset distances which model external markers including skin motion. The fitting process is formulated as an optimization problem minimizing the quadratic error between the tips of the sliders and the measured marker positions. The paper also discusses some simplifications of this approach.

PAMM, 2003

This paper describes an application of multibody dynamics to the determination of global physical... more This paper describes an application of multibody dynamics to the determination of global physical behavior patterns that mimic traditional empirical laws. The main idea is to sift out such patterns from virtual experiments carried out with a simulation package. The concrete investigation in this setting is the dynamics of trains colliding onto buffer stops. Using a rigid-body model with nonlinear couplers featuring hysteresis, it is shown that, for typical train constellations, the highest load at the buffer stops is almost independent of the number of coaches, and that the value and the location of the maximum force within the train does not increase from a particular train length on. These results are compared with traditional formulas for dimensioning of buffer stops used in rail-vehicle industry.

Volume 6A: 37th Mechanisms and Robotics Conference, 2013

ABSTRACT It is very important to synthesize as many feasible kinematic structures of mechanisms a... more ABSTRACT It is very important to synthesize as many feasible kinematic structures of mechanisms as possible in the conceptual design of mechanisms. Besides simple joint mechanisms, multiple joint mechanisms are also widely used in various mechanical systems. This paper proposes an automatic method for the synthesis of planar multiple joint kinematic chains which are seldom addressed in literature. The bicolor topological graph and the bicolor contracted graph are adopted to represent the topological structures of multiple joint kinematic chains. The characteristic number string of bicolor topological graphs is proposed and used to detect efficiently isomorphism in the synthesis progress. A systematic method for the synthesis of kinematic chains with one multiple joint is proposed, and the whole families of multiple joint kinematic chains with up to 16 links and all possible degrees of freedom are obtained for the first time.

Mechanisms and Machine Science, 2015

ABSTRACT Drive simulators using serial robots, such as the KUKA robot “Robocoaster”, are becoming... more ABSTRACT Drive simulators using serial robots, such as the KUKA robot “Robocoaster”, are becoming attractive for situations in which the workspace of traditional Stewart platforms is not suited to accommodate large target rotations, allowing for a wider range of possibilities. Nevertheless—even when using serial robots—the exact target motion can often not be exactly reproduced. In these cases, motion cueing algorithms (MCA) are used to produce a motion which feels as realistic as possible while remaining in the robot acceleration workspace. This paper analyzes the numerical properties of all currently existing MCA (classical, adaptive, optimal, and model predictive control) and selects the most suitable MCA using objective criteria. It also introduces a new procedure for tuning the optimal MCA such that it behaves as good as and even better than much more involved techniques based on the model predictive control (MPC). The new algorithm, termed ZyRo-K, shows best properties for reproducing the desired linear specific force while reducing the rotational false cues. While the work shown in this paper is restricted to numerical evaluation using state-of-the-art “goodness” metrics, the application and test of the algorithms for human passengers on a Robocoaster is currently being prepared and will be published in the near future.

Latest Advances in Robot Kinematics, 2012

ABSTRACT The determination of rigid or overconstrained subsystems is an important task in the cre... more ABSTRACT The determination of rigid or overconstrained subsystems is an important task in the creative design of robotic mechanisms and in the processing of CAD-generated models. While for planar mechanisms with planar graphs a number of methods have been proposed, the case of general spatial mechanisms is still an open topic. In this paper, a novel method for identifying rigid subsystems is presented. The method uses the independent loops as building blocks of a graph, called kinematical network, which describes the overall transmission behavior. The detection of rigid subsystems can then be realized by finding the minimal cutsets in the solution flow of the kinematical network. The method is independent of the subspace in which the bodies are moving, i.e., it is possible to mix planar, spherical and spatial systems. Moreover, it is fast, as only the implicitly coupled loops need to be processed, which comprise much less elements than the number of bodies.