Tension vector and structure matrix associated force sensitivity of a 6-DOF cable-driven parallel robot

This paper investigates the force sensitivity of 6-DOF cable-driven parallel robots (CDPRs) in order to propose a better force measurement device. Kinematics and dynamics for a CDPR of n-DOF are deduced and formulated, and algorithms for calculating the cable tension are developed. Then, by defining geometrical parameters related to the dimensions and configurations of the CDPRs, optimal methods for determining force sensitivity with respect to the structure matrix and twist vector of the 6-DOF CDPRs with two different moving platforms (i.e. a cubic-shaped, and a flat moving platform) are proposed. By using numerical examples integrated with external twists obtained from wind tunnel tests, simulations and analysis for the two type of 6-DOF CDPRs are carried out. The simulation results help identify the optimal dimensions that can be used to design 6-DOF-CDPR-based force measuring devices with high force sensitivity. Experiment validation is also conducted to verify the method proposed in this paper

Optimization in Dynamical Systems: Theory and Application

In this dissertation, we study optimization methods in interconnected systems and investigate their applications in robotics, energy harvesting, and mean-field linear quadratic multi-agent systems. We first focus on parallel robots. Parallel Robots have numerous applications in motion simulation systems and high-precision instruments. Specifically, we investigate the forward kinematics (FK) of parallel robots and formulate it as an error minimization problem. Following this formulation, we develop an optimization algorithm to solve FK and provide a theoretical analysis of the convergence of the proposed algorithm. Then, we investigate the energy optimization (maximization) in a specific class of micro-energy harvesters (MEH). These types of energy harvesters are known to extract the largest amount of power from the kinetic energy of the human body, making them an appropriate choice for wearable technology in healthcare applications. Employing machine learning tools and using the existing models for the MEH's kinematics, we propose three methods for energy maximization. Next, we study optimal control in a mean-field linear quadratic system. Mean-field systems have critical applications in approximating very large-scale systems' behavior. Specifically, we establish results on the convergence of policy gradient (PG) methods to the optimal solution in a mean-field linear quadratic game. We finally consider the risk-constrained control of agents in a mean-field linear quadratic setting. Simulations validate the theoretical findings and their effectiveness

A study to implement a 2D laser scanner to determine the platform position and orientation of a cable robot for logistic applications

Der Einsatz seilgetriebener Parallelmanipulatoren (CDPR) in der Industrie ist der Weg in eine vielversprechende Zukunft. Im Vergleich zum klassischen Parallelmanipulator hat der CDPR einen größeren Arbeitsraum und verbraucht dennoch weniger Energie. Ein CDPR-Prototyp für die Anwendung im Hochregallager wurde im Lehrstuhl für Mechatronik der Universität Duisburg-Essen entwickelt. Ziel ist, diese Anwendung auf den Markt zu bringen. Für die Roboterkalibrierung, zur Bewertung der Roboterregelung und aus Gründen der Sicherheit muss die Position und Orientierung (Pose) der CABLAR-Plattform bestimmt werden. Aktuelle Forschungsarbeiten zeigen, dass die effektivsten Verfahren zur Bestimmung der Plattformpose die direkte Messung mit einem externen Sensor und die indirekte Messung mit einem integrierten Sensor am Seilroboter sind. Beispiele für die direkte und indirekte Messung sind das Kamerasystem und die Vorwärtskinematik. Aufgrund der hohen Kosten ist das Kamerasystem für diese Anwendung weniger geeignet. Andererseits birgt auch die Vorwärtskinematik einige Nachteile: Die aktuelle Geometrie des Roboters stimmt wahrscheinlich wegen der Herstellungs- und/oder Montagetoleranz nicht mit dem kinematischen Modell überein. Zudem beeinflussen Umweltfaktoren, wie z. B. die Temperatur, und eine lange Betriebszeit die Seileigenschaften (z. B. Elastizitätsmodul, Seildichte, Durchmesser). Diese Änderungen verringern die Genauigkeit der Plattformpositionierung. Ein alternatives Verfahren zur Bestimmung der Plattformpose ist die Messung mittels eines 2D-Laserscanners und eines Orientierungsaufnehmers (IMU). In Kombination mit Reflektoren an der linken, rechten und spezielle Anordnung an oberen Seite des Roboterrahmens liefert der Laserscanner einzigartige Messdaten. Das Messergebnis des Laserscanners basiert auf dem Gerade-Ebene-Schnittpunkt, der mittels Gradientenprojektionsverfahren modelliert wird. Zudem wurde ein Kompensationsalgorithmus entwickelt, um die Auswirkung des Geschwindigkeitseffekts auf das Messergebnis aufgrund der Plattformbewegung zu verringern. Der Näherungswert der normalen Parametrierung aller Reflektoren wird mittels der modizierten Hough-Transformation geschätzt. Unter Zuhilfenahme dieses Wertes wurde das Messergebnis anhand eines zufälligen Stichprobenverfahrens (RANSAC Algorithmus, englisch Random Sample Consensus) segmentiert. Ziel ist, die Messdaten der Reflektoren an der linken, rechten, und oberen Seite des Roboterrahmens zu trennen. Die Methode der kleinsten Quadrate (KQ-Methode) bestimmt anhand dieser segmentierten Messdaten den besten Wert der normalen Parametrierung jeder Geraden, die zu allen Reflektoren gehört. Aus diesen Werten werden die y- und z-Komponente und der Rollwinkel der Plattformpose bestimmt. Um die Messfähigkeit des 2D-Laserscanners vom zwei dimensionalen zum räumlichen Messen zu erweitern, wurde ein mathematisches Modell mittels einer speziellen Reflektoranordnung entwickelt. Ziel ist die Bestimmung der x-Komponente und des Gierwinkels der Plattformpose. Der Nickwinkel wird vom IMU gemessen. Die Simulation der Plattform wurde in Ruhe und in Bewegung durchgeführt. Die Simulationsergebnisse sind als Empfehlung für den Versuch am Prototyp zu sehen. Vor dem Versuch wurde die passende Sensorschnittstelle gewählt und getestet. Zudem erfolgte die Gestaltung des Sensorkonzepts zur Datenübertragung. Der Treiber für die Sensoren und die Software für die Datenbearbeitung wurden vorbereitet und das vorgeschlagene Verfahren zur Bestimmung der Plattformpose am Prototyp getestet. Im Versuch wurde die translatorische Komponente der Plattformpose mit direkter Messung der Plattformposition validiert. Der Vergleich zeigt, dass die gemessene Plattformpose nicht an gewünschter Stelle liegt. Danach wurde das vorgeschlagene Verfahren zur Bestimmung der Plattformpose während niedriger und hoher Plattformgeschwindigkeit getestet. Das Ergebnis zeigt, dass dieses Verfahren zur Bestimmung der aktuellen Plattformpose geeignet ist. Die oben beschriebenen Forschungsergebnisse zeigen, dass vorgeschlagene Messverfahren sich zur Bestimmung der Plattformpose in Ruhe und in Bewegung eignet. Aufgrund des günstigen Preises ist das vorgeschlagene Messsystem eine vielsprechende Möglichkeit, die in der kommerziellen Anwendung des CABLAR eingesetzt werden kann.The implementation of a Cable Driven Parallel Robot (CDPR) as a commercial product has a promising future due to its energy efficiency and larger workspace compared to conventional parallel manipulators. A prototype of a CDPR for warehouse applications called CABLAR has been developed at the Chair of Mechatronics at the University of Duisburg-Essen (UDE), which aims to develop the CDPR as a commercial product. In order to benchmark the controller and calibrate the robot, for safety reasons, the platform position and orientation (pose) of the CABLAR must be measured. The current reported approaches to determine the platform pose of a cable robot are direct measurement and indirect measurement. An external sensor such as a camera system or laser tracker is used in direct measurement. Meanwhile, indirect measurement is the determination of the platform pose by forward kinematics where the input is from the proprioceptive sensor. However, the camera system is not worth implementing in the commercial product due to its high cost. On the other hand, forward kinematics has drawbacks when the defined parameters are not identical to the actual parameters. The manufacturing tolerance, assembly tolerance or changing the properties and diameter of the cable because of environmental effects (e.g. temperature) and long operation time are the reasons for this and are difficult to avoid. As a result, the actual pose of the platform could deviate from the desired pose. In this thesis, a direct measurement method by combining a 2D laser scanner with an Inertial Measurement Unit (IMU) is proposed. Several flat reflectors are fixed on the left and right of the robot frame with a special pattern design on the upper side. The laser scanner measurement result during the operation of the CABLAR is imitated based on the line-plane intersection according to the gradient projection method. A compensation algorithm aimed at reducing the velocity effect on the measurement result due to platform motion is proposed. The rough value of normal parametrization of each reflector is estimated using the Modified Hough Transform (mHT) from the measurement result. According to the rough value of the normal parametrization, the measurement result is segmented into a dataset corresponding to the left-, right- and upper-side reflectors by Random Sample Consensus (RANSAC). The linear least squares method is applied in order to determine the ne value of the normal parametrization of all segmented data. The y-component, z-component and roll angle of the platform pose are determined from the fine normal parametrization. A mathematical model based on the reflector special pattern design is developed. The goal is to extend the limitation of the 2D laser scanner from plane measurement to become space measurement in order to obtain the x-component and the yaw angle of the platform pose. The pitch angle is measured by the IMU. The CABLAR model is simulated to verify the proposed measurement method for the conditions where the platform is stationary and in motion. According to the simulation results, several points are concluded as the recommendations for the experiment. Before the experiment was conducted, the suitable hardware interface of the sensors was chosen and tested. The system architecture of the data transfer was designed. The software to drive the sensors and to process the measurement data was prepared. In the experiment on the prototype, the translational components of the platform pose were validated with the direct measurement. Meanwhile the rotational components obtained from the proposed method were validated with the measurement result from the IMU. The results show that the platform position deviates from the desired pose. Furthermore, the proposed platform pose measurement method is tested for the platform in low- and high-velocity motion. The results show that the proposed measurement method is able to determine the actual platform pose. Finally, the proposed measurement method is able to determine the platform pose when stationary and in motion. The proposed measurement system is suitable for application in the commercial CABLAR due its low cost compared to the actual reported measurement system

Function Design of Mechatronic Systems for Human-Robot Collaboration

Traditionally, robots have been caged off from human activity but, recently, improvements in advance robotic technology as well as the introduction of new safety standards, have allowed the possibility of collaboration between human workers and robotic systems. The introduction of Human-Robot Collaboration has the potential to increase the quality and the flexibility of the production process while improving the working condition of the operators. However, traditional industrial robots are typically characterized by small payload and small reachable workspace that reduce the range of possible applications. These drawbacks can overcome the advantages related to a collaborative task and make the collaboration not effective. This work aims at analyzing innovative mechatronic solutions capable of increasing the workspace and the versatility of the system with the final goal of creating effective collaborations with humans. Cable driven Parallel Robots (CDPRs) are considered a promising technology able to satisfy these requirements. In fact, compared to rigid serial and parallel robots, they have several advantages such as large workspaces, high payloads per unit of weight, ease of construction, versatility and affordable costs. This work presents two innovative solutions of CDPR able to enlarge the workspace, improve the versatility and reduce the collisions risk. The first solution consists of a cable-suspended parallel robot with a reconfigurable end-effector whereas the second solution is an innovative model of cable-driven micro-macro robot. In the first part of the thesis, the kinematic and dynamic models of these innovative systems are presented and analyzed in order to characterize their capability. Trajectory planning and optimal design are addressed with the purpose of maximizing the performance of the systems. The last part of the thesis deals with the design of a novel family of Intelligent CAble-driven parallel roBOTs whose architecture and control are conceived to maximize the robot versatility to the task to be performed and the environment in which the robot is intended to operate