Rotation symmetry axes and the quality index in a 3D octahedral parallel robot manipulator system

The geometry of a 3D octahedral parallel robot manipulator system is specified in terms of two rigid octahedral structures (the fixed and moving platforms) and six actuation legs. The symmetry of the system is exploited to determine the behaviour of (a new version of) the quality index for various motions. The main results are presented graphically

Appropriate Design of Parallel Manipulators

International audienceAlthough parallel structures have found a niche market in many applications such as machine tools, telescope positioning or food packaging, they are not as successful as expected. The main reason of this relative lack of success is that the study and hardware of parallel structures have clearly not reached the same level of completeness than the one of serial structures. Among the main issues that have to be addressed, the design problem is crucial. Indeed, the performances that can be expected from a parallel robot are heavily dependent upon the choice of the mechanical structure and even more from its dimensioning. In this chapter, we show that classical design methodologies are not appropriate for such closed-loop mechanism and examine what alternatives are possible

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

An Overview of Kinematic and Calibration Models Using Internal/External Sensors or Constraints to Improve the Behavior of Spatial Parallel Mechanisms

This paper presents an overview of the literature on kinematic and calibration models of parallel mechanisms, the influence of sensors in the mechanism accuracy and parallel mechanisms used as sensors. The most relevant classifications to obtain and solve kinematic models and to identify geometric and non-geometric parameters in the calibration of parallel robots are discussed, examining the advantages and disadvantages of each method, presenting new trends and identifying unsolved problems. This overview tries to answer and show the solutions developed by the most up-to-date research to some of the most frequent questions that appear in the modelling of a parallel mechanism, such as how to measure, the number of sensors and necessary configurations, the type and influence of errors or the number of necessary parameters

Design and control of stewart platform

Demand on high precision motion has been increasing in recent years. Since performance of today's many mechanical systems requires high stiffness and accurate positioning capability, parallel manipulators gained popularity. Their superior architecture provides better load capacity and positioning accuracy over the serial ones. In this work, a popular parallel manipulator, Stewart Platform, has been studied. Stewart Platform is a positioning system that consists of a top plate (moving platform), a bottom plate (fixed base), and six extensible legs connecting the top plate to the bottom plate. This work includes design, analysis, control and testing of a complete positioning system. In order to achieve better accuracy over commonly used universal joints, magnets and spherical joints have been employed in the architecture. Flexure joints have been also analyzed to achieve higher precision levels. Because they eliminate friction and backlash, flexure joints would give better results than universal and spherical joints. Therefore, a parametric study for optimum hyperbolic flexure joints has been also presented. Desired performance of the proposed platform is six degrees of freedom with 500 nm minimum incremental motion. System uncertainties and inherent nonlinearities have been eliminated using sliding mode control. This type of control methodology allows stability in the presence of parametric uncertainties and external disturbances. Although analyses indicate system capability of less than 1 nm resolution, real performance is typically lower due to manufacturing imperfections and measurements errors. The proposed model has been analyzed and tested through simulations, and verified via experiments on a designed and constructed sample Stewart Platform. Laser measurements have been used to measure positional accuracy. System has demonstrated positional accuracy better than the desired 500 nm target performance value