We present a small strain beam model based on the Arbitrary Lagrangian Eulerian setting for use in multibody dynamics. The key contribution of the present paper is to provide a formulation with large flexible reference motion and small overlaid deflections. We point out that the reference motion is described by actual degrees of freedom of the model. Therefore, we use a vector of generalized positions and an Eulerian coordinate, which itself is a degree of freedom and in which the flow of the beam material through an arbitrary volume is represented. The additional displacements describe small fluctuations around the reference motion. With this idea it is easy to separate the motion of belt drives, cable and rope ways or strings. In particular, the overlaid deflections are described for efficient numeric computation and may be analyzed in an easy way for vibrational behavior. The guiding reference motion is arbitrary, i.e., the transmission ratios are degrees of freedom and may change dynamically affecting also the fluctuations. Contacts with dry friction are foreseen and represented in the present model. It is validated and proven to be efficient in comparison with classic co-rotational and absolute nodal coordinate formulations in our application. The simulation of pushbelt continuously variable transmissions is taken as a high-dimensional industrial example.

The exploitation of new fields of application in addition to traditional industrial production for robot manipulators (e.g. agriculture, human areas) requires extensions to the sensor as well as to the planning capabilities. Motion planning solely based on visual information performs poorly in cluttered environments since contacts with obstacles might be inevitable and thus a distinction between hard and soft objects has to be made. In our contribution we present a novel intrinsic tactile sensing module mounted on a multipurpose 9 DOF agricultural manipulator. With its innovative sensor arrangement we consider it to be a low-cost, easily manageable and efficient solution with a reasonable abstraction layer in comparison to complex torque sensing or tactile skins. The sensor provides information about the resulting force and torque. In the second part of our paper, the tactile information is used for minimizing contact forces while pursuing the end-effector tasks as long as reasonable. Hence, we present robust and efficient extensions to Resolved Motion Rate Control for real-time application. We introduce a general formulation providing control inputs in task-space, joint-space and nullspace. Thus, we design a suitable controller by feedback linearization and feed-forward terms. Results from real-world experiments show the potential of our approach. A discussion of the different control schemes completes the paper.

In the EU-funded CROPS project robots are developed for site-specific spraying and selective harvesting of fruit and fruit vegetables. The robots are being designed to harvest crops, such as greenhouse vegetables, apples, grapes and for canopy spraying in orchards and for precision target spraying in grape vines. Attention is paid to the detection of obstacles for autonomous navigation in a safe way in plantations and forests. For the different applications, platforms were built. Sensing systems and vision algorithms have been developed. For software the Robot Operating System is used. A 9 degrees of freedom manipulator was designed and tested for sweet-pepper harvesting, apple harvesting and in close range spraying. For the applications different end-effectors were designed and tested. For sweet pepper a platform that can move in between the crop rows on the common greenhouse rail system which also serves as heating pipes was built. The apple harvesting platform is based on a current mechanical grape harvester. In discussion with growers so-called 'walls of fruit trees' have been designed which bring robots closer to the practice. A canopy-optimised sprayer has been designed as a trailed sprayer with a centrifugal blower. All the applications have been tested under practical conditions.

(a) A pushbelt CVT with elements, loop-sets and pulley sheaves. r x̄, ξ, s

Selective tasks such as harvesting or spraying of single crops are a promising research topic in agricultural automation. Inspired by industrial production, an obvious approach is to use robot manipulators in greenhouses and orchards. To exploit the potential of redundant manipulators in particular, advanced motion planning algorithms are needed. While harvesting, a new trajectory for every fruit has to be planned. Although the scenario is similar for every fruit, it is unique for each harvesting sequence. In this paper we present an efficient online planning approach which takes advantage of a simplified environment model. However, the generated trajectory is not optimal in general w.r.t. joint velocities or might even be unfeasible. Thus, we introduce an optional global offline optimization scheme which is able to find optimal trajectories in a few seconds and takes advantage of the heuristic planning as initial guess. We apply the proposed scheme to a 9-DOF agricultural manipulator for sweet-pepper harvesting and evaluate our method by extensive tests with fruit positions based on real measurements.

Centrifugal pendulum vibration absorbers are used to attenuate steady-state torsional vibrations in rotating and reciprocating machines. In most practical implementations, a set of multiple absorbers is symmetrically arranged on a rotor. Typically, each absorber mass is bifilar suspended, which allows the absorber mass to be moved along a prescribed path. Previous studies have considered how to determine absorber paths in order to obtain absorbers with amplitude independent frequency known as tautochronic absorbers. It is known that a tautochronic absorber is highly desirable if only one absorber is installed on the rotor. However, in most applications multiple interacting absorbers are installed and as a result symmetry induced nonlinear instabilities or localization caused by relative imperfections among the absorbers may occur. An effective strategy to avoid such situations is to perturb the tautochronic tuning which has been confirmed in practice and by previous theoretical investigations.This paper presents an approach for del:Lining a recently developed general Lautochronic absorber design. The general design makes it possible to consider a wide class of Lautochronic absorbers, e.g. absorbers without bifilar suspensions. The intent of this paper is to extend the existing tautochronic design guideline to non-Lautochronic designs. As a result, different absorber designs can be addressed by one uniform theoretical approach, and existing absorber designs are included as special cases. Former studies On detuning of bifilar tautochronic absorbers use a one-parameter family of curves on which the absorber mass rides. Here, however, the detuning is not restricted to a one-parameter family of curves, which makes it possible to either optimize system performance or to avoid asynchronous absorber responses. In the case of synchronously responding equal absorbers, a necessary condition for optimal performance is derived analytically. Further, it is shown that asynchronous responses can be avoided by applying positive detuning. (C) 2014 Elsevier Ltd. All rights reserved.

Single-Port Surgery is a recent development in minimally invasive surgery and denotes abdominal surgery where all instruments are inserted through a single incision. Further progress in the field of surgical intervention can solely be achieved by combined benefits regarding both surgical and technical improvements.The reduction of trauma as well as improvements in ergonomics compared to laparoscopic surgery can be recognized as main objectives. To comply with these requirements, a real-time controlled mechatronic-assisted single-port manipulator SISTUM with sufficient workspace and applied forces for precise tissue manipulation is proposed. With regard to sterility and biocompatibility aspects, the manipulating part of this system the bio-inspired bending structure - is manufactured using selective laser sintering (SLS) with biocompatible polymers.

Condition monitoring is vital for operating rotors safely. The application of model-based approaches allows a more detailed diagnosis than signal-based methods. Yet, model-based methods require identifying the properties of the undamaged rotor accurately. Measurements at single parts and modal analysis help to verify the rotor model. When monitoring rotor displacements with eddy-current sensors, also roundness errors must be considered. For roundness identification at operation speed, a method based on three non-orthogonal eddy-current sensors is presented. Several experiments show that the measurement data can be split into the contents rotor orbit and roundness error. The extracted orbit is evaluated by an academic model-based monitoring system developed for our test rig. Currently, it can evaluate unbalance, bow, misalignments and/or stator contact.

A system for automatic model-based monitoring of multiple coexistent errors is being developed. Within this publication, the unsteady bow curve of a test rig rotor is examined. For simulating this rotor, the bow model of the Jeffcott rotor is expanded to a MDOF rotor. The application of the Ritz approach enriched with problem-specific shape functions leads to an accurate simulation with low numerical effort. The bow model and the monitoring scheme are successfully tested. Bow, unbalance and roundness error can be identified separately during normal operation of the rotor.

In multibody simulation, the Gear–Gupta–Leimkuhler method or stabilized index 2 formulation for persistent contacts enforces constraints on position and velocity level at the same time. It yields a robust numerical discretization of differential algebraic equations avoiding the drift-off effect and is often more effective than decreasing the time step size to preserve geometric characteristics. In this work, we carry over these benefits to impacting mechanical systems with unilateral constraints. For this kind of a mechanical system, adding the position level constraint to an (event-capturing) timestepping scheme on velocity level even maintains physical consistency of the impulsive discretization. Hence, we propose a timestepping scheme based on Moreau’s midpoint rule, which enables to achieve not only compliance of the impact law, but also of the nonpenetration constraint. The choice of a decoupled and consecutive evaluation of the respective constraints can be interpreted as a not energy-consistent coordinate projection to the nonpenetration constraint at the end of each time step. It is the implicit coupling of position and velocity level, which yields satisfactory results. An implicit evaluation of the right hand side improves stability properties without additional cost. With the prox function formulation, the overall set of nonsmooth equations is solved by a nonsmooth Newton method. Results from simulations of a slider-crank mechanism with unilateral constraints demonstrate the capability of our approach.

The drive mechanism of many robot joints are composed of an electrical actuator and a gear transmission. Besides actuator dynamics and gear elasticity, friction effects are of particular importance for accurate dynamic modeling. This paper presents the design and development of a modular testbed for experimental friction identification in modular robot drives. We have used this testbed to investigate modules that were developed at our institute for the humanoid robot Lola and an agricultural manipulator. We discovered that a friction law, similar to a law proposed in the literature, can be very accurately fitted to our measurements.

Determining the optimal solution for the inverse kinematics of redundant robots has been the focus of much previous research. Instantaneous approaches are computationally efficient, but may cause high joint velocities due to their local character. In this paper, we present an efficient implementation of a global approach following Pontryagin's Minimum Principle for online calculation. Within a moving horizon, we exploit the decoupled structure of the resulting optimal control problem by using the conjugate gradient method for solving the nonlinear dynamic problem. Different examples of cost functionals are presented and the real-time capability is shown by applying this approach to a 9-DOF redundant manipulator.

In the EU-funded CROPS (Clever Robots for Crops) project high tech robots are developed for site-specific spraying and selective harvesting of fruit and fruit vegetables. The harvesting robots are being designed to harvest high-value crops such as greenhouse vegetables, fruits in orchards and grapes for premium wines. The CROPS robots are also developed for canopy spraying in orchards and for precision target spraying in grape vines to reduce the use of pesticides. A CROPS robot will be able to detect the fruit, sense its ripeness, then move to grasp and gently detach only the ripe fruit. For crop protection the canopy sprayer can detect contours of trees in an orchard and consequently only spraying on the trees and the precision target sprayer can detect diseases on leaves of vine grapes and only spray pesticides on the affected spots of the leaves. In the CROPS project also attention is paid to reliable detection and classification of objects and obstacles for autonomous navigation in a safe way in plantations and forests. For the several applications within the CROPS project platforms were developed. Sensing systems and appropriate vision algorithms for the platforms have been developed. For the software platform the Robot Operating System (ROS) is used. A 9 degrees of freedom (DOF) manipulator was designed and built and tested for sweet-pepper harvesting, apple harvesting and in close range spraying. The 9-DOF manipulator is modular, since the joint configuration can be adapted to the applications, e.g. 6 DOF for the close range spraying. For the different applications different end-effectors were designed and tested. The main results of the CROPS project will be the applications, the so-called demonstrators For sweet pepper a platform that can move in between the crop rows on the common greenhouse rail system which also serves as heating pipes was built and equipped with a sensing and lightning system, the manipulator and end-effectors. The complete system was tested and showed to growers in a lab situation. The apple harvesting platform is based on a current mechanical grape harvester. In discussion with growers so-called 'walls of fruit trees' have been designed which bring robots closer to the practice. This system, equipped with a sensing system the CROPS manipulator and a special end-effector, has been successfully tested in an orchard. A canopy-optimised sprayer has been designed as a trailed sprayer with a centrifugal blower. The system has been successfully tested in an orchard with a significant reduction of pesticide use. For close range target spraying the spraying robot in a greenhouse experiment with grape vines reduced the pesticide consumption with 84%.

Implicit integration methods are often used for numerically stiff multi-body systems in order to reduce the timestep-size. But within most implicit integration methods, the jacobian of the right hand side must be calculated at every step. In case of multi-body dynamics, this is the vector of generalized forces and the calculation of its jacobian can be so expensive, that it often outweighs the advantage of a bigger step-size. For large systems, this task can take more than 99% of the whole simulation time, while it can be easily parallelized. In this paper, a hybrid-parallel implementation of calculating this jacobian is presented. With a combination of MPI and OpenMP, simulations on up to 512 cores are run. The experiments are carried out on a high-performance-computing cluster with an infiniband network. The performance of a pure MPI implementation is compared to several hybrid variants, using different numbers of OpenMP threads per process.

Since the 1930s, centrifugal pendulum vibration absorbers have been used in rotating and reciprocating machinery for the attenuation of torsional vibrations. A large variety of absorber types were suggested and the design was done by linearization theory until the introduction of the tautochronic bifilar pendulum absorbers. Since then, the performance and dynamic stability of this specific absorber type have been considered in analytical and numerical investigations. Different perturbations, e.g. nonlinear mistuning, were considered in order to optimize the system performance, but the characteristic bifilar design remained unchanged. In this paper, a general approach for the design of tautochronic pendulum vibration absorbers is proposed. As a result, it is possible to deal with a large variety of non-bifilar centrifugal vibration absorber designs which provide application-related optimal performance and resolve some of the existing design limitations.Established analytic predictions that show a satisfactory agreement with numerical as well as experimental investigations for bifilar absorbers are not applicable for the comparison of different tautochronic absorbers. Therefore, the second part of this work shows how to analyze this class of centrifugal vibration absorbers using a Hamiltonian formulation. Successive canonical transformations lead to nonlinear equations in action-angle variables, which are then approximated to first order and analyzed by using the method of averaging. These results provide a basis for the design and analysis of tautochronic bifilar and non-bifilar vibration absorbers. (C) 2013 Elsevier Ltd. All rights reserved.

In recent years, a lot of research and development has been done in the field of autonomous harvesting in agriculture. For bulk harvesting and spraying applications (e.g. grape harvesting), there already are commercially available systems. However, automation for selective harvesting (i.e., picking) of single fruits and precision spraying applications remain challenging. Contrary to common industrial automation applications, the unstructured environment of agricultural processes lead to high demands on the design of the sensory system, the machinery in general and the planning algorithms. In our contribution we will address the path planning task for a modular agricultural manipulator with redundant kinematics. We will describe two approaches for automatically generating a path in the manipulator workspace: (1) a heuristic approach with low requirements on sensor information and (2) a potential field approach. Since the environment in agriculture applications is usually compliant (e.g. leaves or branches) only major obstacles (i.e. stems and fruits) are taken into account. The obstacles are represented by primitive objects, like cylinders and spheres. Notably, all planning algorithms are suitable for real time applications. The algorithms are implemented on a robot, which was designed and manufactured during the CROPS project. It is a prototype for the harvesting of sweet-peppers, apples and grapes, as well as the precision spraying of grapes. The suitability of the algorithms will be demonstrated in a lab environment and recommendations from experiments of first field test will be discussed. As a further result, the paper will bring out the limitations, advantages and disadvantages of the proposed approaches.

Exploration of virtual worlds with unconstrained locomotion possibilities for the user is the main objective of the European research project CyberWalk. This should be achieved through the use of an actuated platform (the CyberCarpet) that compensates for the walker's locomotion in such a way to keep her/him close to the platform center. This paper presents the control problem for the platform motion, including objectives and constraints, overall control architecture, and kinematic modeling. Since the platform has only two actuating devices (linear and angular), the control problem is similar to that of output regulation for nonholonomic wheeled mobile robots in the presence of an unpredictable disturbance due to walker's locomotion. Based on the kinematic model, a velocity control design achieving input-output decoupling and linearization is proposed and its performance is verified by simulations