Reconfigurable cable driven parallel mechanism

Due to the fast growth in industry and in order to reduce manufacturing budget, increase the quality of products and increase the accuracy of manufactured products in addition to assure the safety of workers, people relied on mechanisms for such purposes. Recently, cable driven parallel mechanisms (CDPMs) have attracted much attention due to their many advantages over conventional parallel mechanisms, such as the significantly large workspace and the dynamics capacity. In addition, it has lower mass compared to other parallel mechanisms because of its negligible mass cables compared to the rigid links. In many applications it is required that human interact with machines and robots to achieve tasks precisely and accurately. Therefore, a new domain of scientific research has been introduced, that is human robot interaction, where operators can share the same workspace with robots and machines such as cable driven mechanisms. One of the main requirements due to this interaction that robots should respond to human actions in accurate, harmless way. In addition, the trajectory of the end effector is coming now from the operator and it is very essential that the initial trajectory is kept unchanged to perform tasks such assembly, operating or pick and place while avoiding the cables to interfere with each other or collide with the operator. Accordingly, many issues have been raised such as control, vibrations and stability due the contact between human and robot. Also, one of the most important issues is to guarantee collision free space (to avoid collision between cables and operator and to avoid collisions between cables itself). The aim of this research project is to model, design, analysis and implement reconfigurable six degrees of freedom parallel mechanism driven by eight cables. The main contribution of this work will be as follow. First, develop a nonlinear model and solve the forward and inverse kinematics issue of a fully constrained CDPM given that the attachment points on the rails are moving vertically (conventional cable driven mechanisms have fixed attachment points on the rails) while controlling the cable lengths. Second, the new idea of reconfiguration is then used to avoid interference between cables and between cables and operator limbs in real time by moving one cable’s attachment point on the frame to increase the shortest distance between them while keeping the trajectory of the end effector unchanged. Third, the new proposed approach was tested by creating a simulated intended cable-cable and cable-human interference trajectory, hence detecting and avoiding cable-cable and cable-human collision using the proposed real time reconfiguration while maintaining the initial end effector trajectory. Fourth, study the effect of relocating the attachment points on the constant-orientation wrench feasible workspace of the CDPM. En raison de la croissance de la demande de produits personnalisés et de la nécessité de réduire les coûts de fabrication tout en augmentant la qualité des produits et en augmentant la personnalisation des produits fabriqués en plus d'assurer la sécurité des travailleurs, les concepteurs se sont appuyés sur des mécanismes robotiques afin d’atteindre ces objectifs. Récemment, les mécanismes parallèles entraînés par câble (MPEC) ont attiré beaucoup d'attention en raison de leurs nombreux avantages par rapport aux mécanismes parallèles conventionnels, tels que l'espace de travail considérablement grand et la capacité dynamique. De plus, ce mécanisme a une masse plus faible par rapport à d'autres mécanismes parallèles en raison de ses câbles de masse négligeable comparativement aux liens rigides. Dans de nombreuses applications, il est nécessaire que l’humain interagisse avec les machines et les robots pour réaliser des tâches avec précision et rapidité. Par conséquent, un nouveau domaine de recherche scientifique a été introduit, à savoir l'interaction humain-robot, où les opérateurs peuvent partager le même espace de travail avec des robots et des machines telles que les mécanismes entraînés par des câbles. L'une des principales exigences en raison de cette interaction que les robots doivent répondre aux actions humaines d'une manière sécuritaire et collaboratif. En conséquence, de nombreux problèmes ont été soulevés tels que la commande et la stabilité dues au contact physique entre l’humain et le robot. Aussi, l'un des enjeux les plus importants est de garantir un espace sans collision (pour éviter les collisions entre des câbles et un opérateur et éviter les collisions entre les câbles entre eux). Le but de ce projet de recherche est de modéliser, concevoir, analyser et mettre en œuvre un mécanisme parallèle reconfigurable à six degrés de liberté entraîné par huit câbles. La principale contribution de ces travaux de recherche est de développer un modèle non linéaire et résolvez le problème de cinématique direct et inverse d'un CDPM entièrement contraint étant donné que les points d'attache sur les rails se déplacent verticalement (les mécanismes entraînés par des câbles conventionnels ont des points d'attache fixes sur les rails) tout en contrôlant les longueurs des câbles. Dans une deuxième étape, l’idée de la reconfiguration est ensuite utilisée pour éviter les interférences entre les câbles et entre les câbles et les membres d’un opérateur en temps réel en déplaçant un point de fixation du câble sur le cadre pour augmenter la distance la plus courte entre eux tout en gardant la trajectoire de l'effecteur terminal inchangée. Troisièmement, la nouvelle approche proposée a été évaluée et testée en créant une trajectoire d'interférence câble-câble et câble-humain simulée, détectant et évitant ainsi les collisions câble-câble et câble-humain en utilisant la reconfiguration en temps réel proposée tout en conservant la trajectoire effectrice finale. Enfin la dernière étape des travaux de recherche consiste à étudiez l'effet du déplacement des points d'attache sur l'espace de travail réalisable du CDPM

Integrated Trajectory-Tracking and Vibration Control of Kinematically-Constrained Warehousing Cable Robots

With the explosion of e-commerce in recent years, there is a strong desire for automated material handling solutions including warehousing robots. Cable driven parallel robots (CDPRs) are a relatively new concept which has yet to be explored for high-speed pick-&-place applications in the industry. Compared to rigid-link parallel robots, a CDPR possesses significant advantages including: large workspace, low moving inertia, high-speed motion, low power consumption, and incurring minimal maintenance cost. On the other hand, the main disadvantages of the CDPRs are the cable’s unilateral force exerting capability and low rigidity which is resulting in undesired vibrations of their moving platform. Kinematically-constrained CDPRs (KC-CDPRs) include a special class of CDPRs which provide a considerably higher level of stiffness in undesired degrees of freedom (DOFs) via connecting a set of constrained cables to the same actuator. Nevertheless, undesired vibrations of the moving platform are still their main problem which request more attention and investigation. Dynamic modeling, stiffness optimization, vibration and trajectory-tracking control, and stiffness-based trajectory-planning of redundant KC-CDPRs are studied in this thesis. As a new technique, we separate the moving platform’s vibration equations from its desired (nominal) equations of motion. The obtained vibration model forms a linear parametric variable (LPV) dynamic system which is based for the following contributions: 1) Proposing a new tension optimization approach to minimize undesired perturbations under external disturbances in a desired direction; and demonstrating the effectiveness of kinematically-constrained actuation method in vibration attenuation of CDPRs in undesired DOFs. 2) Providing the opportunity of using a wide class of well-established robust and optimal LPV-based control methods, such as H∞ control techniques, for trajectory-tracking control of CDPRs to minimize the effect of disturbances on the robot operation; and showing the effectiveness of kinematically-constrained actuation method in control design simplification of such robots. 3) Proposing the concept of stiffness-based trajectory-planning to find the stiffness-optimum geometry of trajectories for KC-CDPRs; and designing a time-optimal zero-to-zero continuous-jerk motion to track such trajectories. All the proposed concepts are developed for a generic KC-CDPR and verified via numerical analysis and experimental tests of a real planar warehousing KC-CDPR

Robotic System Development for Precision MRI-Guided Needle-Based Interventions

This dissertation describes the development of a methodology for implementing robotic systems for interventional procedures under intraoperative Magnetic Resonance Imaging (MRI) guidance. MRI is an ideal imaging modality for surgical guidance of diagnostic and therapeutic procedures, thanks to its ability to perform high resolution, real-time, and high soft tissue contrast imaging without ionizing radiation. However, the strong magnetic field and sensitivity to radio frequency signals, as well as tightly confined scanner bore render great challenges to developing robotic systems within MRI environment. Discussed are potential solutions to address engineering topics related to development of MRI-compatible electro-mechanical systems and modeling of steerable needle interventions. A robotic framework is developed based on a modular design approach, supporting varying MRI-guided interventional procedures, with stereotactic neurosurgery and prostate cancer therapy as two driving exemplary applications. A piezoelectrically actuated electro-mechanical system is designed to provide precise needle placement in the bore of the scanner under interactive MRI-guidance, while overcoming the challenges inherent to MRI-guided procedures. This work presents the development of the robotic system in the aspects of requirements definition, clinical work flow development, mechanism optimization, control system design and experimental evaluation. A steerable needle is beneficial for interventional procedures with its capability to produce curved path, avoiding anatomical obstacles or compensating for needle placement errors. Two kinds of steerable needles are discussed, i.e. asymmetric-tip needle and concentric-tube cannula. A novel Gaussian-based ContinUous Rotation and Variable-curvature (CURV) model is proposed to steer asymmetric-tip needle, which enables variable curvature of the needle trajectory with independent control of needle rotation and insertion. While concentric-tube cannula is suitable for clinical applications where a curved trajectory is needed without relying on tissue interaction force. This dissertation addresses fundamental challenges in developing and deploying MRI-compatible robotic systems, and enables the technologies for MRI-guided needle-based interventions. This study applied and evaluated these techniques to a system for prostate biopsy that is currently in clinical trials, developed a neurosurgery robot prototype for interstitial thermal therapy of brain cancer under MRI guidance, and demonstrated needle steering using both asymmetric tip and pre-bent concentric-tube cannula approaches on a testbed

Increasing the Automation Level of Serial Robotic Manipulators with Optimal Design and Collision-free Path Control

The current hydraulic robotic manipulator mechanisms for heavy-duty machines are a mature technology, and their kinematics has been developed with a focus on the human operator maneuvering a hydraulically controlled system without numerical control input. As the trend in heavy-duty manipulators is increased automation, computer control systems are increasingly being widely used, and the requirements for robotic manipulator kinematics are different. Computer control enables a different kind of robotic manipulator kinematics, which is not optimum for direct control by a human operator, because the joint motions related to the different trajectories are not native for the human mind. Numerically controlled robotic manipulators can accept kinematics that is more efficient at doing the job expected by the customer.To increase the autonomous level of robotic manipulator, the optimal structure is not enough, but it is a part of the solution toward a fully autonomous manipulator. The control system of the manipulator is the main part of computer-controlled manipulators. A collision avoidance system plays an important role in the field of autonomous robotics. Without collision avoidance functionality, it is quite obvious that only very simple movements and tasks can be carried out automatically. With more complicated movement and manipulators, some kind of collision avoidance system is required. An unknown or changing environment increases the need for an intelligent collision avoidance system that can find a collision-free path in a dynamic environment.This thesis deals with these fundamental challenges by optimizing the serial manipulator structure for the desired task and proposing a collision avoidance control system. The basic requirement in the design of such a robotic manipulator is to make sure that all the desired task points can be achieved without singularities. These properties are difficult to achieve with the general shape and type of robotic manipulators. In this research work, a task-based kinematic synthesis approach with the proper optimization method ensures that the desired requirements can be fulfilled.To enable autonomous task execution for robotic manipulators, the control systems must have a collision avoidance system that can prevent different kinds of collisions. These collisions include self-collisions, collisions with other manipulators, collisions with obstacles, and collisions with the environment. Furthermore, there can be multiple simultaneous possible collisions that need to prevented, and the collision system must be able to handle all these collisions in real-time. In this research work, a real-time collision avoidance control approach is proposed to handle these issues. Overall, both topics, covered in this thesis, are believed to be key elements for increasing the automation of serial robotic manipulators

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications

Design, modelling and control of a brachiating power line inspection robot

The inspection of power lines and associated hardware is vital to ensuring the reliability of the transmission and distribution network. The repetitive nature of the inspection tasks present a unique opportunity for the introduction of robotic platforms, which offer the ability to perform more systematic and detailed inspection than traditional methods. This lends itself to improved asset management automation, cost-effectiveness and safety for the operating crew. This dissertation presents the development of a prototype industrial brachiating robot. The robot is mechanically simple and capable of dynamically negotiating obstacles by brachiating. This is an improvement over current robotic platforms, which employ slow, high power static schemes for obstacle negotiation. Mathematical models of the robot were derived to understand the underlying dynamics of the system. These models were then used in the generation of optimal trajectories, using nonlinear optimisation techniques, for brachiating past line hardware. A physical robot was designed and manufactured to validate the brachiation manoeuvre. The robot was designed following classic mechanical design principles, with emphasis on functional design and robustness. System identification was used to capture the plant uncertainty and a feedback controller was designed to track the reference trajectory allowing for energy optimal brachiation swings. Finally, the robot was tested, starting with sub-system testing and ending with testing of a brachiation manoeuvre proving the prospective viability of the robot in an industrial environment

Teleprogramming: Overcoming Communication Delays in Remote Manipulation (Dissertation Proposal)

Modern industrial processes (nuclear, chemical industry), public service needs (firefighting, rescuing), and research interests (undersea, outer space exploration) have established a clear need to perform work remotely. Whereas a purely autonomous manipulative capability would solve the problem, its realization is beyond the state of the art in robotics [Stark et al.,1988]. Some of the problems plaguing the development of autonomous systems are: a) anticipation, detection, and correction of the multitude of possible error conditions arising during task execution, b) development of general strategy planning techniques transcending any particular limited task domain, c) providing the robot system with real-time adaptive behavior to accommodate changes in the remote environment, d) allowing for on-line learning and performance improvement through experience , etc. The classical approach to tackle some of these problems has been to introduce problem solvers and expert systems as part of the remote robot workcell control system. However, such systems tend to be limited in scope (to remain intellectually and implementationally manageable), too slow to be useful in real-time robot task execution, and generally fail to adequately represent and model the complexities of the real world environment. These problems become particularly severe when only partial information about the remote environment is available

Model Based Teleoperation to Eliminate Feedback Delay NSF Grant BCS89-01352 First Report

We are conducting research in the area of teleoperation with feedback delay. Delay occurs with earth-based teleoperation in space and with surface-based teleoperation with untethered submersibles when acoustic communication links are involved. the delay in obtaining position and force feedback from remote slave arms makes teleoperation extremely difficult. We are proposing a novel combination of graphics and manipulator programming to solve the problem by interfacing a teleoperator master arm to a graphics based simulator of the remote environment coupled with a robot manipulator at the remote, delayed site. the operator\u27s actions will be monitored to provide both kinesthetic and visual feedback and to generate symbolic motion commands to the remote slave. the slave robot will then execute these symbolic commands delayed in time. While much of a task will proceed error free, when an error does occur the slave system will transmit data back to the master and the master environment will be reset to the error state