Jan Brinker

Design methodology for translational parallel manipulators exhibiting actuation redundancy

In general, spatial manipulation of objects can be accomplished by parallel manipulators, whose number of actuators is equal to the demanded number of degrees of freedom. In order to improve, for example, positioning accuracy, stiffness characteristics, and transmission behavior, redundant drives can be added to the manipulator. Accordingly, this paper presents a methodology for the design of a translational parallel manipulator with redundant actuation. Based on the results of systematic structural syntheses and developed selection criteria, two valid configurations (i.e. 3-PŘŘŘ and 3-PUU) are analyzed. Since feasibility and performance of these configurations are dependent on the base geometry, five types of base geometries are introduced. First, the geometric parameters of each of the resulting 10 combinations of nonredundant configurations and base geometries are optimized by minimizing the maximal actuation force within a prescribed workspace. Second, the best combinations are used to generate redundant configurations with six legs. These redundant configurations are then analyzed with respect to the potential of improvement concerning homogenization of end-effector forces using force polytopes. It is shown that redundant actuation significantly improves the distribution of end-effector forces. This improvement has a positive influence on positioning accuracy and acceleration capabilities. In addition to these aspects, for further analysis it is planned to investigate the influence of homogenized end-effector forces on the dimensioning of actuators and finally on the energy efficiency of the entire configuration.

On the Motion/Force Transmissibility and Constrainability of Delta Parallel Robots

The motion and force transmission is highly important for the analysis and design of parallel manipulators. Recent advances in research have led to generally applicable formulations for transmission indices based on the notion of power coefficient. Analyses of limited-dof parallel manipulators however require separate consideration of constraint characteristics. Conversely, the design parameters of parallel manipulators are highly coupled. Thus, such separation may distort the performance evaluation and optimization of parallel manipulators. In this context, indices based on pressure angles of fully parallel manipulators are revisited and applied to the performance evaluation of the Delta robot, one of the lower-dof parallel robots. The resulting index is physically appropriate and allows for simultaneous assessment of both, the motion and force transmission and the constraint characteristics.

AutoHD—Automated Handling and Draping of Reinforcing Textiles

In almost all industrial sectors handling processes are automated through the use of robotic systems. However, in the manufacture of fiber-reinforced structures with complex geometries, the handling of dry, pre-impregnated semi-finished textiles is still performed mainly manually resulting in long processing times, low reproducibility and high manufacturing costs. A previous AiF research project “AutoPreforms” aimed at the automation of the entire production process of components with uniaxial curvature. The scope of this AiF research project “AutoHD” is to fully automate the draping and handling process of complex, three-dimensional fiber composite structures with high degrees of deformation and multiaxial curvature (e.g. car wings). Based on a draping simulation wrinkles can already be recognized during the draping process and counteracted by the developed mechanical structure. This is achieved by the utilization of the bending stiffness of textile semi-finished products, a flexible end-effector and a built-in optical quality assurance process. In this paper the main aspects of preforming processes are described revealing the challenges of the project. With examples of currently existing systems, the objective and innovative contribution of the project are described. The paper serves as initial presentation of the project and its solution approaches.

Comparative Study of Serial-Parallel Delta Robots With Full Orientation Capabilities

More than thirty years after the initial concepts, commercial Delta and Delta-like robots serve a niche market for high-speed pick-and-place applications. Expired patents and new fields of application have led to increased research and innovative designs. By functionally extending the original translational Delta robot with additional serial chains, commercial concepts obtain up to three additional rotational degrees-of-freedom. In this context, the paper in hand is concerned with the analyses of serial-parallel Delta robots with full orientation capabilities. Based on efficient kinematic relations, an energy-related dynamic model is derived for four potential extensions. By solving the inverse dynamic problem, the influences of the additional serial chains on the actuation torques of the basic parallel Delta robot are analyzed. Furthermore, the merits of each individual concept are evaluated using torque-related indices (i.e., energy consumption and root mean square torque) and discussed from a design point of view. It is shown that two types of extensions are predestined for industrial application. In these variants, the wrist motors are either attached to the frame or to the distal links.

Synthesis and Modeling of Redundantly Actuated Parallel Kinematic Manipulators—An Approach to Efficient Motion Design

Spatial object manipulation is subject to various parameters, which can be optimized by means of suitable motion strategies. In addition, corresponding strategies can be adapted to specified handling devices enabling efficient motion design with respect to kinematic and dynamic characteristics of particular manipulators. Further optimization is provided by the application of robot redundancy, whose resolution can be adapted to efficient motion planning. In this context, parallel kinematic systems featuring kinematic redundancy or a redundant actuator concept can be operated with an optimal set of actuator parameters allowing a resource-efficient object manipulation. This contribution is devoted to the conception and modeling of redundantly actuated parallel kinematic manipulators (RA-PKM) in order to realize optimal configuration strategies and motion design. Accordingly, the structure selection and the dimensional synthesis of a translational RA-PKM are presented based on parametric kinematic and dynamic modeling. Corresponding models provide an application-oriented transformation from intuitive CAD design software to technical computing and simulation software. The developed manipulator is suitable for the comparison of different redundant and non-redundant actuator configurations as well as optimal trajectories. Concluding analyses exemplarily refer to a non-redundant 3-arm and a redundant n-arm PRPaR system.

Lagrangian Based Dynamic Analyses of Delta Robots with Serial-Parallel Architecture

30 years after the initial concepts, commercial Delta and Delta-like robots serve a niche market for high-speed pick-and-place applications. Expired patents and new fields of applications have led to increased research and development in recent years. The increased scientific focus on extended architectures with additional rotational dof resulted in different serial-parallel hybrid as well as fully-parallel designs. These concepts meet the industrial demands for novel complex handling tasks, increased payload capacities, and hygienic designs. This contribution presents kinematic and energy-based dynamic analyses for the classical Delta structure and six different extensions. Based on that, the required computation times and the influences of inertial effects are investigated.

Mechanism Type Synthesis Approach for Automated Handling and Multiaxial Draping of Reinforcing Textiles

This contribution is concerned with the first design step for an end-effector used to fully automate the draping and handling process of complex, three-dimensional fibre composite structures with high degrees of deformation and multiaxial curvature. A demonstrator part was specified representing common challenges of draping, e.g., multiaxial complex shape including varying edges and curves of different radii. Analyses of the required draping movements provide information on the motion task and the resulting requirements. Based on that and for the selection of mechanisms for translational motions, a set of criteria is defined and comprehensive evaluation methods are applied. In this context, this contribution employs the outcome of previous systematic type syntheses of translational parallel manipulators. The aim of this contribution is to identify feasible mechanisms to be integrated into the overall system design.

Stiffness Analysis of Delta Parallel Robots Combining the Virtual Joint Method with an FEA Stiffness Model

In this paper a stiffness analysis approach for Delta parallel robots is presented, which combines the Virtual Joint Method (VJM) with a Finite Element Analysis (FEA) stiffness model of the proximal link. By comparison with a purely analytical model and measurements it is shown that using this more laborious combination of VJM and FEA is reasonable in early stages of the robot design process.

Dynamic Modeling of Functionally Extended Delta-Like Parallel Robots with Virtual Tree Structures

Depending on the modeling approach, dynamic analyses of parallel robots often involve expensive computations of undesired constraint forces, cumbersome partial derivatives, or large matrix operations. Decomposing the parallel structure into virtual tree structures and the free platform allows for reducing the system size as well as efficient recursive and parallel computing. Against this background, the Khalil-Ibrahim Method is adapted to the well-known Delta parallel robot. It is shown that the resulting model deftly removes constraint forces while being modularly expandable for analyzing recent design modifications using additional serial chains attached to the parallel Delta structure.

A Study on Simplified Dynamic Modeling Approaches of Delta Parallel Robots

This contribution presents a study on simplified dynamic modeling approaches of the Delta parallel robot . Complete and simplified dynamic modeling approaches are reviewed and compared in respect to their computation times. Also, the dependency of the accuracy on the mass distribution of the distal link is analyzed in detail and assessed based on a single industry-relevant pick-and-place trajectory as well as randomly generated Lissajous curves for (more) general validity.