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

Redundant Unilaterally Actuated Kinematic Chains: Modeling and Analysis

Unilaterally Actuated Robots (UAR)s are a class of robots defined by an actuation that is constrained to a single sign. Cable robots, grasping, fixturing and tensegrity systems are certain applications of UARs. In recent years, there has been increasing interest in robotic and other mechanical systems actuated or constrained by cables. In such systems, an individual constraint is applied to a body of the mechanism in the form of a pure force which can change its magnitude but cannot reverse its direction. This uni-directional actuation complicates the design of cable-driven robots and can result in limited performance. Cable Driven Parallel Robot (CDPR)s are a class of parallel mechanisms where the actuating legs are replaced by cables. CDPRs benefit from the higher payload to weight ratio and increased rigidity. There is growing interest in the cable actuation of multibody systems. There are potential applications for such mechanisms where low moving inertia is required. Cable-driven serial kinematic chain (CDSKC) are mechanisms where the rigid links form a serial kinematic chain and the cables are arranged in a parallel configuration. CDSKC benefits from the dexterity of the serial mechanisms and the actuation advantages of cable-driven manipulators. Firstly, the kinematic modeling of CDSKC is presented, with a focus on different types of cable routings. A geometric approach based on convex cones is utilized to develop novel cable actuation schemes. The cable routing scheme and architecture have a significant effect on the performance of the robot resulting in a limited workspace and high cable forces required to perform a desired task. A novel cable routing scheme is proposed to reduce the number of actuating cables. The internal routing scheme is where, in addition to being externally routed, the cable can be re-routed internally within the link. This type of routing can be considered as the most generalized form of the multi-segment pass-through routing scheme where a cable segment can be attached within the same link. Secondly, the analysis for CDSKCs require extensions from single link CDPRs to consider different routings. The conditions to satisfy wrench-closure and the workspace analysis of different multi-link unilateral manipulators are investigated. Due to redundant and constrained actuation, it is possible for a motion to be either infeasible or the desired motion can be produced by an infinite number of different actuation profiles. The motion generation of the CDSKCs with a minimal number of actuating cables is studied. The static stiffness evaluation of CDSKCs with different routing topologies and isotropic stiffness conditions were investigated. The dexterity and wrench-based metrics were evaluated throughout the mechanism's workspace. Through this thesis, the fundamental tools required in studying cable-driven serial kinematic chains have been presented. The results of this work highlight the potential of using CDSKCs in bio-inspired systems and tensegrity robots

Design and analysis of a parallel mechanism for kinematically redundant hybrid planar laser cutting machine

Conventional planar laser cutting machines cannot achieve high accelerations, because the required precision values cannot be achieved due to the high inertial loads. Machines configured as kinematically redundant mechanisms are able to reach 5-6 g acceleration levels since they include a parallel mechanism with a smaller workspace which is exposed to smaller inertial loads. The study presented in this paper focuses on the design of a parallel planar mechanism to be integrated to the main axes of conventional planar laser cutting machines to achieve higher accelerations of the laser head up to 6 g. Parallel mechanism’s conceptual design and dynamic balancing studies are provided along with the joint clearance effect on precision due to having more joint structures.Republic of Turkey Ministry of Science, Industry and Technology & Coşkunöz Metal Form (Project code: 01668.STZ.2012-2

Wrench capability of planar manipulators

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2016.Robôs são amplamente utilizados em fábricas, e novas aplicações no espaço, nos oceanos, nas indústrias nucleares e em outros campos estão sendo ativamente desenvolvidas. A criação de robôs autônomos que podem aprender a agir em ambientes imprevisíveis têm sido um objetivo de longa data da robótica, da inteligência artificial, e das ciências cognitivas.Um passo importante para a autonomia dos robôs é a necessidade de dotá-los com um certo nível de independência, a fim de enfrentar as mudanças rápidas no ambiente circundante; para obter robôs que operem fora de ambientes rigidamente estruturados, tais como centros de investigação ou instalações de universidades e sem precisar da supervisão de engenheiros ou especialistas, é necessário enfrentar diferentes desafios tecnológicos, entre eles, o desenvolvimento de estratégias que permitam que os robôs interajam com o ambiente. Neste contexto, quando um contacto físico com o ambiente é estabelecido, uma força específica precisa de ser exercida e esta força tem de ser controlada em relação ao processo a fim de evitar a sobrecarga ou danificar o manipulador ou os objetos a serem manipulados.O principal objetivo deste trabalho é apresentar novas metodologias desenvolvidas para determinar a máxima carga que um mecanismo ou manipulador planar pode aplicar ou suportar (capacidade de carga), sejam eles paralelos, seriais ou híbridos e com redundância ou não. A fim de resolver o problema da capacidade de carga, neste trabalho foram propostas duas novas abordagens com base no método do fator de escala clássico e nos métodos clássicos de otimização. Essas novas abordagens deram como resultado um novo método chamado de método de fator de escala modificado utilizado para resolver a capacidade de carga em manipuladores seriais planares e quatro modelos matemáticos para resolver o problema de capacidade de carga em manipuladores paralelos planares com um grau líquido de restrição igual três, quatro, cinco ou seis (CN = 3, CN = 4, CN = 5 ou CN = 6).Abstract : Robots are now widely used in factories, and new applications of robots in space, the oceans, nuclear industries, and other fields are being actively developed. Creating autonomous robots that can learn to act in unpredictable environments has been a long-standing goal of robotics, artificial intelligence, and cognitive sciences.An important step towards the autonomy of robots is the need to provide them with a certain level of independence in order to face quick changes in the environment surrounding them; to get robots operating outside rigidly structured environments, such as research centres or universities facilities and beyond the supervision of engineers or experts, it is necessary to face different technological challenges, amongst them, the development of strategies that allow robots to interact with the environment. In this context, when a physical contact with the the environment is established, a process-specific force need to be exerted and this force has to be controlled in relation to the particular process in order to prevent overloading or damaging the manipulator or the objects to be manipulated.The main objective of this work is to present new methodologies developed for determining the maximum wrench that can be applied or sustained (wrench capability) in planar mechanisms and manipulators, whether it be serial parallel or hybrid and with redundancy or not. In order to solve the wrench capability problem, in this work two new approaches were proposed based in the classic scaling factor method and in classical optimization methods. These new approaches gave as result a new method called the modified scaling factor method used to solve the wrench capability in planar serial manipulators and four mathematical closed-form solutions to solve the wrench capability problem in planar parallel manipulators with a net degree of constraint equal to three, four, five or six (CN = 3, CN = 4, CN = 5 ou CN = 6)

A bibliometric overview of Mechanism and Machine Theory journal: publication trends from 1990 to 2020

This work reports a bibliometric overview of Mechanism and Machine Theory journal in the timespan 1990-2020. This desideratum is achieved by considering the most relevant features associated with the life of this scientific journal, namely in terms of publications, citations, regions of origin of publications, authors, institutions, etc. In the present study, the Scopus database was chosen as the platform to identify and extract information on those aspects. Thus, based on the data collected, a comprehensive bibliometric analysis of Mechanism and Machine Theory is performed, which permits to reveal the overall picture of the journal trends in evolution, as well as its impact and influence in the mechanism and machine science community. Overall, the outcomes presented in this study allow to observe that Mechanism and Machine Theory journal has been attracting more and more interest year after year.FCT -Fundação para a Ciência e a Tecnologia(UIDB/04436/2020

Design and Hierarchical Force-Position Control of Redundant Pneumatic Muscles-Cable-Driven Ankle Rehabilitation Robot

Ankle dysfunction is common in the public following injuries, especially for stroke patients. Most of the current robotic ankle rehabilitation devices are driven by rigid actuators and have problems such as limited degrees of freedom, lack of safety and compliance, and poor flexibility. In this letter, we design a new type of compliant ankle rehabilitation robot redundantly driven by pneumatic muscles (PMs) and cables to provide full range of motion and torque ability for the human ankle with enhanced safety and adaptability, attributing to the PM's high power/mass ratio, good flexibility and lightweight advantages. The ankle joint can be compliantly driven by the robot with full three degrees of freedom to perform the dorsiflexion/plantarflexion, inversion/ eversion, and adduction/abduction training. In order to keep all PMs and cables in tension which is essential to ensure the robot's controllability and patient's safety, Karush-Kuhn-Tucker (KKT) theorem and analytic-iterative algorithm are utilized to realize a hierarchical force-position control (HFPC) scheme with optimal force distribution for the redundant compliant robot. Experiment results demonstrate that all PMs are kept in tension during the control while the position tracking accuracy of the robot is acceptable, which ensures controllability and stability throughout the compliant robot-assisted rehabilitation training

Inverse Dynamics of a Redundantly Actuated Four-Bar Mechanism Using an Optimal Control Formulation

This paper presents an approach to estimating joint torques in a four-bar closed-chain mechanism with prescribed kinematics and redundant actuation, i.e., with more actuators than degrees of freedom. This problem has several applications in industrial robots, machine tools, and biomechanics. The inverse dynamics problem is formulated as an optimal control problem (OCP). The dynamical equations are derived for an open-chain mechanism, what keeps the formulation simple and straightforward. Sets of constraints are explored to force the three-link open-chain to behave as a four-bar mechanism with a crank rotating at a constant velocity. The controls calculated from the OCP are assumed to be the input joint torques. The standard case with one torque actuator is solved and compared to cases with two and three actuators. The case of two actuators presented the smallest peak and mean torques, using one specific set of constraints. Such torques were smaller than the solution obtained using an alternative method existing in literature that solves the redundancy problem by means of the pseudo-inverse matrix. Comparison with inverse dynamics solutions using well-established methods for the one-actuator closedloop four-bar were equal. Reconstructed kinematical trajectories from forward integration of the closed-loop mechanism with the OCP obtained torques were essentially similar. The results suggest that the adopted procedure is promising, giving solutions with lower torque requirements than the regularly actuated case and redundantly actuated computed with other approaches. The applicability of the method has been shown for the four-bar mechanism. Other classes of redundantly actuated, closed-loop mechanisms could be tested using a similar formulation. However, the numerical parameters of the OCP must be chosen carefully to achieve convergence