Application of the Rotation Matrix Natural Invariants to Impedance Control of Rotational Parallel Robots

Force control of parallel robots with rotational degrees of freedom through impedance algorithms is considerably influenced by the representation method of the end-effector orientation. Using the natural invariants of the rotation matrix and the angular velocity vector in the impedance control law has some theoretical advantages, which derive from the Euclidean-geometric meaning of these entities. These benefits are particularly evident in case of robotic architectures with three rotational degrees of freedom (serial or parallel wrists with spherical motion). The behaviour of a 3-CPU parallel robot controlled by an impedance algorithm based on this concepts is assessed through multibody simulations, and the results confirm the effectiveness of the proposed approach

An Image-Based Real-Time Georeferencing Scheme for a UAV Based on a New Angular Parametrization

Simultaneous localization and mapping (SLAM) of a monocular projective camera installed on an unmanned aerial vehicle (UAV) is a challenging task in photogrammetry, computer vision, and robotics. This paper presents a novel real-time monocular SLAM solution for UAV applications. It is based on two steps: consecutive construction of the UAV path, and adjacent strip connection. Consecutive construction rapidly estimates the UAV path by sequentially connecting incoming images to a network of connected images. A multilevel pyramid matching is proposed for this step that contains a sub-window matching using high-resolution images. The sub-window matching increases the frequency of tie points by propagating locations of matched sub-windows that leads to a list of high-frequency tie points while keeping the execution time relatively low. A sparse bundle block adjustment (BBA) is employed to optimize the initial path by considering nuisance parameters. System calibration parameters with respect to global navigation satellite system (GNSS) and inertial navigation system (INS) are optionally considered in the BBA model for direct georeferencing. Ground control points and checkpoints are optionally included in the model for georeferencing and quality control. Adjacent strip connection is enabled by an overlap analysis to further improve connectivity of local networks. A novel angular parametrization based on spherical rotation coordinate system is presented to address the gimbal lock singularity of BBA. Our results suggest that the proposed scheme is a precise real-time monocular SLAM solution for a UAV.Peer reviewe

Six-DOF impedance control based on angle/axis representations

Impedance control is a well-established framework to manage the interaction of the end effector of a robot manipulator with the environment, For the execution of six-degree-of-freedom (DOF) tasks, both the end-effector position and orientation must be handled. The operational space control schemes typically utilize minimal representations of end-effector orientation; however, such representations do not lead to a physically meaningful definition of the rotational part of the impedance equation, and they suffer from the occurrence of representation singularities. In this work a new approach to six-DOF impedance control is proposed, where the end-effector orientation displacement is derived from the rotation matrix expressing the mutual orientation between the compliant frame and the desired frame, An alternative Euler angles-based description is proposed which mitigates the effects of representation singularities. Then, a class of angle/axis representations are considered to derive the dynamic equation for the rotational part of a six-DOF impedance at the end effector, using an energy-based argument. The unit quaternion representation is selected to further analyze the properties of the rotational impedance, The resulting impedance controllers are designed according to an inverse dynamics strategy with contact force and moment measurements, where an inner loop acting on the end-effector position and orientation error is adopted to confer robustness to unmodeled dynamics and external disturbances. Experiments on an industrial robot with open control architecture and force/torque sensor have been carried out, and the results in a number of case studies are discussed

Six-DOF impedance control based on angle/axis representations

A new approach to 6-DOF impedance control is proposed, where the end-effector orientation displacement is derived from the rotation matrix expressing the mutual orientation between the compliant frame and the desired frame. An alternative Euler angles-based description is proposed which mitigates the effects of representation singularities. Then, a class of angle/axis representations are considered to derive the dynamic equation for the rotational part of a 6-DOF impedance at the end effector, using an energy-based argument. The unit quaternion representation is selected to further analyze the properties of the rotational impedance. The resulting impedance controllers are designed according to an inverse dynamics strategy with contact force and moment measurements, where an inner loop acting on the end-effector position and orientation error is adopted to confer robustness to unmodeled dynamics and external disturbances. Experiments on an industrial robot were carried out, and the results of case studies are discusse

Six-DOF impedance control based on angle/axis representations

Impedance control is a well-established framework to manage the interaction of the end effector of a robot manipulator with the environment, For the execution of six-degree-of-freedom (DOF) tasks, both the end-effector position and orientation must be handled. The operational space control schemes typically utilize minimal representations of end-effector orientation; however, such representations do not lead to a physically meaningful definition of the rotational part of the impedance equation, and they suffer from the occurrence of representation singularities. In this work a new approach to six-DOF impedance control is proposed, where the end-effector orientation displacement is derived from the rotation matrix expressing the mutual orientation between the compliant frame and the desired frame, An alternative Euler angles-based description is proposed which mitigates the effects of representation singularities. Then, a class of angle/axis representations are considered to derive the dynamic equation for the rotational part of a six-DOF impedance at the end effector, using an energy-based argument. The unit quaternion representation is selected to further analyze the properties of the rotational impedance, The resulting impedance controllers are designed according to an inverse dynamics strategy with contact force and moment measurements, where an inner loop acting on the end-effector position and orientation error is adopted to confer robustness to unmodeled dynamics and external disturbances. Experiments on an industrial robot with open control architecture and force/torque sensor have been carried out, and the results in a number of case studies are discussed

Extraction methods for multidirectional driving point accelerance and transfer point accelerance matrices

To experimentally determine the multidirectional driving point and transfer accelerance matrices is a difficult task that has remained unsolved for 30 years. These matrices relate both linear and rotational degrees of freedom in three dimensions. The direct measurement of dynamic moments and rotational accelerations is very difficult. Little work exists on the subject and none includes so many DOF\u27s. Besides, it is assumed that any test attachment is rigid and none used angular accelerometers to measure the angular acceleration;Various errors in substructure testing are studied. The study reveals that the interface DOF deficiency error is the most catastrophic and sophisticated error. None of interfacial DOF\u27s can be neglected. The bias error can be corrected easily. The noise error appears to be most severe in the low frequency range. The exciter rocking motion leads to incorrect bare vehicle transmissibility matrix and incorrect global transmissibility matrix. The driving point difference error increases quickly as the distance between the impact and measurement points increases;The DOF deficiency error has several sources. It comes from the difference between the inverse from a complete interface model and the inverse of a reduced interface model. It also comes from the deletion of cross coupling terms between the neglected motions and remaining forces, the neglected forces and the remaining motions, and the neglected forces and the neglected motions;A number of numerical-experimental hybrid measurement methods are proposed and evaluated for finding the multidirectional driving point and transfer point accelerance matrices in both 2D and 3D. These methods are tested for their robustness under conditions of noisy data. A 2D implementation, called a T-bar, and a 3D implementation, called a C-bar, of an elastic test attachment structure, called Instrument Cluster , are developed. Accelerometers are embedded in the Instrument Cluster . The finite element model is an integral part of the experimental testing process. The FE FRF\u27s of the Instrument Cluster are used together with the experimental FRF\u27s of the combined structure. A new rotational accelerometer is used to obtain better rotational acceleration than two closely spaced linear accelerometers. Experimental results show this method is both feasible and promising

Controle de impedância em robôs manipuladores

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.Este trabalho tem como objetivo estudar o uso do controle de impedância no controle de um robô manipulador rígido. No trabalho é abordada a aplicação do controle de impedância implementado a partir de um controle de posição, através da inclusão de uma realimentação de esforço/torque, de maneira a tornar a impedância apresentada pelo manipulador exclusivamente dependente do controle. O desempenho do controle de impedância na forma desenvolvida é verificado em simulações numéricas para o caso do controle de um manipulador SCARA, considerando a sua estrutura completa. São simuladas movimentações no espaço livre e em contato com o meio, para a situação real e com variação paramétrica. O controle de impedância é implementado no manipulador SCARA Inter do laboratório de Robótica da Universidade Federal de Santa Catarina, utilizando a linguagem de programação Xoberon. Seu desempenho é comparado com os resultados obtidos nas simulações

Kraftsensorlose Manipulator Kraftsteuerung zur Abtastung unbekannter, harter Oberflächen

Die vorliegende Arbeit zeigt ein Verfahren zur kraftgesteuerten Kontaktierung unbekannter harter Freiformflächen mit einem Standard–6DOF-Industriemanipulator (z.B. Manutec R2). Die bisher entwickelten Verfahren auf dem Gebiet der Manipulatorkraftregelung waren auf teure, fragile, mehrdimensionale Kraft-/Momentensensoren am Manipulator-Endeffektor angewiesen, die bei dem in dieser Arbeit entwickelten Ansatz der sensorlosen Kraft-/Geschwindigkeitsregelung überflüssig werden. Die Einstellung der gewünschten Kontaktkraft zu der unbekannten Umgebung erfolgt ausschließlich über eine robuste, beobachtergestützte Regelung der Motorströme der Gelenkantriebe. In freien Bewegungsphasen garantierte eine kaskadierte Kraft-/Geschwindigkeitsregelung vordefinierte Heranfahrgeschwindigkeiten an die unbekannte Kontaktoberfläche. Hierdurch eröffnen sich vollkommen neue Einsatzszenarien für die kraftkontrollierte Kontaktierung und Bearbeitung unbekannter Oberflächen oder Werkstücke beliebiger Härte und Steifigkeit

Control and Learning of Compliant Manipulation Skills

Humans demonstrate an impressive capability to manipulate fragile objects without damaging them, graciously controlling the force and position of hands or tools. Traditionally, robotics has favored position control over force control to produce fast, accurate and repeatable motion. For extending the applicability of robotic manipulators outside the strictly controlled environments of industrial work cells, position control is inadequate. Tasks that involve contact with objects whose positions are not known with perfect certainty require a controller that regulates the relationship between positional deviations and forces on the robot. This problem is formalized in the impedance control framework, which focuses the robot control problem on the interaction between the robot and its environment. By adjusting the impedance parameters, the behavior of the robot can be adapted to the need of the task. However, it is often difficult to specify formally how the impedance should vary for best performance. Furthermore, fast it can be shown that careless variation of the impedance can lead to unstable regulation or tracking even in free motion. In the first part of the thesis, the problem of how to define a varying impedance for a task is addressed. A haptic human-robot interface that allows a human supervisor to teach impedance variations by physically interacting with the robot during task execution is introduced. It is shown that the interface can be used to enhance the performance in several manipulation tasks. Then, the problem of stable control with varying impedance is addressed. Along with a theoretical discussion on this topic, a sufficient condition for stable varying stiffness and damping is provided. In the second part of the thesis, we explore more complex manipulation scenarios via online generation of the robot trajectory. This is done along two axes 1) learning how to react to contact forces in insertion tasks which are crucial for assembly operations and 2) autonomous Dynamical Systems (DS) for motion representation with the capability to encode a family of trajectories rather than a fixed, time-dependent reference. A novel framework for task representation using DS is introduced, termed Locally Modulated Dynamical Systems (LMDS). LMDS differs from existing DS estimation algorithms in that it supports non-parametric and incremental learning all the while guaranteeing that the resulting DS is globally stable at an attractor point. To combine the advantages of DS motion generation with impedance control, a novel controller for tasks described by first order DS is proposed. The controller is passive, and has the properties of an impedance controller with the added flexibility of a DS motion representation instead of a time-indexed trajectory