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Featured researches published by Christoph Woernle.


Journal of Mechanical Design | 1991

A Complete Solution for the Inverse Kinematic Problem of the General 6R Robot Manipulator

H. Y. Lee; Christoph Woernle; Manfred Hiller

The inverse kinematic problem of the general 6R robot manipulator is completely solved by means of a 16th degree polynomial equation in the tangent of the half-angle of a revolute joint. An algorithm is developed to compute the desired joint angles of all possible configurations of the kinematic chain for a given position of the end-effector. Examples for robots with maximal 16 different configurations show that the polynomial degree 16 is the lowest possible for the general 6R robot manipulator. Further, a numerical method for the determination of the boundaries of the workspace and its subspaces with different numbers of configurations is developed. These boundaries indicate the singular positions of the end-effector.


Medical Engineering & Physics | 2013

Generation of physiological parameter sets for hip joint motions and loads during daily life activities for application in wear simulators of the artificial hip joint

Christian Fabry; Sven Herrmann; Michael Kaehler; Ernst-Dieter Klinkenberg; Christoph Woernle; Rainer Bader

At present, wear investigations of total hip replacements are performed in accordance with the ISO standard 14242, which is based on simplified kinematic and force data of the gait cycle. The aim of this analytical study was to generate parameter sets of daily life activities in order to replicate more realistic joint load situations in wear testing. Hence, published in vivo motion and force data of daily life activities were evaluated and adjusted using analytical techniques. The created kinematically and dynamically consistent parameter sets comprised time trajectories of three Cardan angles to describe the motion of the femur with respect to the pelvis and time trajectories of three force components, representing the hip joint contact force. The parameter sets include the activities of walking, knee bending, stair climbing and a combined load case of sitting down and standing up. Additionally, a motion sequence following the frequency of daily life activities was presented. Differences of the evaluated angular motions and joint contact forces in comparison to the ISO standard 14242-1 were pointed out. The results of this study offer the possibility to extend the kinematics and dynamics of the ISO standard test protocol and to support the loading conditions of hip wear simulators with a comprehensive set of motions and loads close to reality.


Mechanism and Machine Theory | 1984

A unified representation of spatial displacements

Manfred Hiller; Christoph Woernle

Abstract The spatial screw displacement of a rigid body can be expressed in terms of points and in terms of lines by real (3 × 3)-matrices and (4 × 4)-matrices for the screw displacement of points, and by dual vectors and tensors, dual-number (3 × 3)-matrices, screw coordinates and dual-number quaternions for the screw displacement of lines. In the present paper it is shown, that finite screw displacements can be obtained by integration of an associate differential equation for the infinitesimal screw displacement. The representation is based on the “screw displacement pair”—the dual-number extension of the rotational displacement pair—and consists of the characteristic parameters of the screw displacement: the dual unit vector of the screw axis and the associate dual angle of the amplitude. From the screw displacement pair, the various mathematical representations for screw displacements, mentioned above, as well as their close connections can easily be derived. By the time derivative of the screw displacement pair, the velocity screw of the instantaneous screw motion can be obtained.


Medical Engineering & Physics | 2014

Dynamic behavior of tripolar hip endoprostheses under physiological conditions and their effect on stability

Christian Fabry; Michael Kaehler; Sven Herrmann; Christoph Woernle; Rainer Bader

Tripolar systems have been implanted to reduce the risk of recurrent dislocation. However, there is little known about the dynamic behavior of tripolar hip endoprostheses under daily life conditions and achieved joint stability. Hence, the objective of this biomechanical study was to examine the in vivo dynamics and dislocation behavior of two types of tripolar systems compared to a standard total hip replacement (THR) with the same outer head diameter. Several load cases of daily life activities were applied to an eccentric and a concentric tripolar system by an industrial robot. During testing, the motion of the intermediate component was measured using a stereo camera system. Additionally, their behavior under different dislocation scenarios was investigated in comparison to a standard THR. For the eccentric tripolar system, the intermediate component demonstrated the shifting into moderate valgus-positions, regardless of the type of movement. This implant showed the highest resisting torque against dislocation in combination with a large range of motion. In contrast, the concentric tripolar system tended to remain in varus-positions and was primarily moved after stem contact. According to the results, eccentric tripolar systems can work well under in vivo conditions and increase hip joint stability in comparison to standard THRs.


Computer Methods and Programs in Biomedicine | 2012

HiL simulation in biomechanics: A new approach for testing total joint replacements

Sven Herrmann; Michael Kaehler; Robert Souffrant; Roman Rachholz; János Zierath; Daniel Kluess; Wolfram Mittelmeier; Christoph Woernle; Rainer Bader

Instability of artificial joints is still one of the most prevalent reasons for revision surgery caused by various influencing factors. In order to investigate instability mechanisms such as dislocation under reproducible, physiologically realistic boundary conditions, a novel test approach is introduced by means of a hardware-in-the-loop (HiL) simulation involving a highly flexible mechatronic test system. In this work, the underlying concept and implementation of all required units is presented enabling comparable investigations of different total hip and knee replacements, respectively. The HiL joint simulator consists of two units: a physical setup composed of a six-axes industrial robot and a numerical multibody model running in real-time. Within the multibody model, the anatomical environment of the considered joint is represented such that the soft tissue response is accounted for during an instability event. Hence, the robot loads and moves the real implant components according to the information provided by the multibody model while transferring back the position and resisting moment recorded. Functionality of the simulator is proved by testing the underlying control principles, and verified by reproducing the dislocation process of a standard total hip replacement. HiL simulations provide a new biomechanical testing tool for analyzing different joint replacement systems with respect to their instability behavior under realistic movements and physiological load conditions.


Volume 7: 2nd Biennial International Conference on Dynamics for Design; 26th International Conference on Design Theory and Methodology | 2014

Load Calculation on Wind Turbines: Validation of Flex5, Alaska/Wind, MSC.Adams and SIMPACK by Means of Field Tests

János Zierath; Roman Rachholz; Christoph Woernle; Andreas Müller

Load calculations on wind turbines are an essential part of its development. In the preliminary design phase simplified multibody models are used for the estimation of the interface loads. The interface loads are used within an iterative development loop to design the components of the wind turbine such as gearbox, blades, tower and so on. Due to the early application of load calculations within the development process, the quality of the simulation results has a great influence on the wind turbine design.In this contribution the simulation results of the multibody codes alaska/Wind, MSC.Adams and SIMPACK are compared with measurements obtained from a prototype of a 2.05 MW wind turbine developed by W2e Wind to Energy. Furthermore, simulation results of the special wind turbine design code Flex5, developed at the Technical University of Denmark Copenhagen, are taken into account. A statistical and dynamical evaluation of the simulation and measurement results has been done. Due to the use of the same controller procedures as used on the physical wind turbine, the wind turbine models show almost the same behaviour (electrical power, pitch angle, rotor speed) as the wind turbine in the field. Differences occur during the evaluation of the interface loads due to the different kinds of wind turbine modelling.Copyright


Archive | 2013

Trajectory Tracking for a Three-Cable Suspension Manipulator by Nonlinear Feedforward and Linear Feedback Control

Christoph Woernle

The kinematically indeterminate cable suspension manipulator Cablev moves a payload platform in space by three spatially arranged cables with independently controllable winches. As the position of the platform is not fully determined by the lengths of the cables, undesired sway motions of the payload platform may occur. To make the payload platform track prescribed translational and rotational reference trajectories in space, a two-stage control concept is presented. A nonlinear feedforward control that exploits the flatness property of the system generates control inputs for the undisturbed motion along reference trajectories. Sway motions caused by disturbances are actively damped by a linear feedback of measured state variables enabling an asymptotically stable tracking behaviour. Experimental results from the prototype system Cablev are shown.


Archive | 2010

Robot-Based HiL Test of Joint Endoprostheses

Christoph Woernle; Michael Kähler; Roman Rachholz; Sven Herrmann; János Zierath; Robert Souffrant; Rainer Bader

To simulate the dislocation behavior of total hip endoprostheses in their anatomical environment a novel Hardware-in-the-Loop (HiL) simulator is built up. It couples a real endoprosthesis with a numerical simulation of its environment by means of an industrial robot as actuator system. The simulation model describes the dynamics of the biomechanical motions including the tissue and muscle forces. The motion and joint constraint forces are calculated by the simulation model and applied to the endoprosthesis by the robot under hybrid position/force control. The actual position of the endoprosthesis in the constrained directions and torques in the unconstrained directions are measured and fed back into the simulation model closing the control loop. To demonstrate the functional principle of the HiL simulator the dynamic behavior of a test setup is numerically simulated.


Archive | 2009

Hardware-in-the-Loop Simulation of Constraint Elements in Mechanical Systems

Michael Kähler; Christoph Woernle; Rainer Bader

To simulate constraint elements of mechanical systems like joints or bearings in their environment a Hardware-in-the-Loop (HiL) simulator is proposed. It couples a real joint with a numerical simulation of its environment by means of an actuator system and sensors. The actual application standing behind this investigation is HiL testing of hip endoprostheses with respect to their dislocation behavior. HiL simulations allow the analysis of real system components in a virtual environment controlled by a computer and are thereby particularly advantageous if test conditions in the real environment of the system component are either too complex or impossible to apply like in vivo investigations of dislocation scenarios. As a preliminary research two fundamental variants for the coupling between the real joint and the simulation of the environment are discussed and experimentally demonstrated.


international conference on robotics and automation | 1988

The characteristic pair of joints-an effective approach for the inverse kinematic problem of robots

Manfred Hiller; Christoph Woernle

The inverse kinematic problem of robot manipulators requires the computation of the joint coordinates to execute prescribed trajectories. It implies the determination of six dependant joint coordinates in a kinematic multibody loop by six nonlinear algebraic constraint equations. The approach presented yields a nonredundant system of constraint equations which is always partitioned into an implicit core system and explicitly solvable equations. General rules have been derived for the generation of these equations. For numerous classes of manipulator designs even the complete system of equations can be solved in closed form. The effectiveness of the method has been proved by several technical applications in cooperation with the West German robot industry.<<ETX>>

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Manfred Hiller

University of Duisburg-Essen

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