Christopher Reichert

A Versatile Tension Distribution Algorithm for

Redundancy resolution of redundantly actuated cable-driven parallel robots (CDPRs) requires the computation of feasible and continuous cable tension distributions along a trajectory. This paper focuses on n-DOF CDPRs driven by n + 2 cables, since, for n = 6, these redundantly actuated CDPRs are relevant in many applications. The set of feasible cable tensions of n-DOF (n + 2)-cable CDPRs is a 2-D convex polygon. An algorithm that determines the vertices of this polygon in a clockwise or counterclockwise order is first introduced. This algorithm is efficient and can deal with infeasibility. It is then pointed out that straightforward modifications of this algorithm allow the determination of various (optimal) cable tension distributions. A self-contained and versatile tension distribution algorithm is thereby obtained. Moreover, the worst-case maximum number of iterations of this algorithm is established. Based on this result, its computational cost is analyzed in detail, showing that the algorithm is efficient and real-time compatible even in the worst case. Finally, experiments on two six-degree-of-freedom eight-cable CDPR prototypes are reported.

n

In this paper an internal force-based impedance controller for redundantly actuated cable-driven parallel robots (CDPRs) is proposed. For CDPRs, each actuated cable forms a manipulator equipped with the feature of an impedance to enforce a dynamical relationship between the end-effector (EE) velocity and the internal forces. No explicit position and force control loops are necessary. This approach can guarantee a desired tension level in the cable system for given EE movements. Additionally the platform dynamics do not cause tracking or steady state position errors. Non-linear effects like model uncertainties take a negative influence on the controller. The incorporated disturbance observers guarantee the necessary robustness for the impedance controller. To validate the described control approach, experiments with a 6-DOF CDPR with industrial BLDC-Motors are presented.

-DOF Parallel Robots Driven by

This paper deals with the problem of computing minimum feasible cable force distributions for redundantly actuated cable-driven parallel robots. In this context, the known Closed Form Method as well as its limitations are presented and potential improvements are identified. This finally leads to an approach called Improved Puncture Method. Then the methods are analyzed regarding their covered workspace, the resulting cable force distributions and the needed computation time. Finally the Improved Puncture Method was implemented into the augmented PD controller and run on the SEGESTA prototype.

n+2

In this chapter geometrical force calculation algorithms, namely the Barycentric Approach, the Weighted Average Approach, the Corner Projection Method, the Closed Form Method and the Puncture Method are discussed. The last four were implemented for a threefold redundancy and their performance regarding their practical applicability is investigated. The analysis includes the covered workspace, the characteristics of the resulting cable forces, the needed computation time and the adaptability to varying degrees of redundancy.

Cables

Conventional automated storage and retrieval systems (AS/RS) are widely used to realize an efficient infrastructure for large warehouses. Nevertheless, they require a lot of energy when performing the storage of goods in high racks. This paper presents a new AS/RS type based on a wire robot technology which is very lightweight and therefore capable for huge energy savings compared to the conventional systems. While wire robots usually create the required wire forces only by electrical motors, the application of counterweights and springs offers additional energy saving potential which is simulated and discussed. Since the computation of the wire forces is usually computationally demanding, the paper also proposes a new real-time-capable and simple method to solve this problem.

Robust Internal Force-Based Impedance Control for Cable-Driven Parallel Robots

This contribution presents an introduction to cable robots, their properties and their mechatronic design for application in automated construction. Today, most steps involved in the construction process are performed manually. Thus, the integration of automated functions demands a closer look at the production and logistic paradigms, these are the main focus of this paper. Based on case studies, the authors discuss upcoming transformations in shell production by comparing the conventional construction process with proposed processes involving cable-driven parallel robots. The focus is on bricklaying and working methods for the installation of prefabricated elements. Adaptations to site logistics and changes in work organization are also considered. A case study and sensitivity analysis based on system dynamics modeling are introduced, and the conceptual design of an experimental prototype is presented. The results of the investigations show that the use of a cable-driven robot is feasible for onsite construction, enabling automation of processes to save time and cost. The study investigates crucial parameters and the potential for cable robots in the field of construction.

Analysis of a Real-Time Capable Cable Force Computation Method

The construction industry is still dominated by manual processes. This is both due to conventional planning tools that do not allow for a complete digital representation of a building and the limitation of the workspace of conventional robots that is far below the dimensions of most buildings. With the introduction of Building Information Modeling (BIM), the first is subject to change. BIM will allow for a holistic representation of any building and thus allow for digital workflows that enable efficient automation. Second, the development of cable-driven parallel robots meanwhile allows to create large manipulators that even cover the volume of a construction site. This allows for automated construction processes. The paper addresses BIM as a base for motion planning, investigates workspace aspects and site layout and introduces an experimental setup for feasibility studies. Initial experimental results are presented and discussed.

Analysis of Geometrical Force Calculation Algorithms for Cable-Driven Parallel Robots with a Threefold Redundancy

This paper addresses multiple strategies to reduce the energy consumption of a rack feeder that is based on cable-driven robot technology. Here, both the hardware design and the trajectories to be followed are optimized.

An energy-efficient wire-based storage and retrieval system

This paper deals with a virtual prototype of spatial redundantly constraint cable-driven parallel robot (CDPR) using object-oriented modeling approach. The main physical components of CDPR such as platform, winches, pulleys and cables are mathematically and object-orientedly modeled in Dymola. The parameters used are based on the SEGESTA prototype which is a spatial type CDPR developed for industrial applications by Chair of Mechatronic, Universitt Duisburg-Essen. The trajectory motion of the virtual prototype is generated by a trajectory planner and controlled using an augmented PD controller in MATLAB Simulink. For the sake of robustness and reliability, the co-simulation procedure is executed with a complex trajectory. Then, the simulation results are analyzed and discussed.