The study of the stiffness of parallel robots is becoming increasingly important to improve the performancein terms of accuracy and precision. Some industrial applications require to maximize the numberof cycles per minute. This results in high acceleration that can be reached only by lightening the movingparts. Materials such as carbon fibers, titanium or aluminum are increasingly used in robotics becausethey combine some of the features of lightness and strength. Nevertheless, the optimization of the materialsis not sufficient to ensure the required performance. Researchers must focus on design and criticalissues that parallel robots may encounter within their workspace.The so-called parallel robots with reduced mobility, i.e. those in which the mobility of the end-effectoris less than six degrees of freedom, often have a number of redundant constraints within their kinematicchains, . In the presence of these deformations robot can change its functionality or not work at alldue to internal locking.Maps based on indices of stiffness might help to better understand how the positioning and orientingerrors vary the workspace, . Stiffness models can be added in the control system in order to providefor a compensation of the errors due to deformations.The importance of the rigidity is also evident for miniature applications. Mini-parallel robots with reducedmobility combined together and are used as assembly stations, as instance for small electroniccomponents, . Often, the small size of links and joints involve high deformations during operation,making the robot impractical to use.To this purpose, the authors propose a linear method to study the stiffness of lower mobility parallelrobots. Only small deformations and displacements are considered. The method is modular and can usedto obtain either symbolic or numeric results, ; besides, avoiding the use of Lagrangian multipliers,joints are included in an implicit way. The proposed formulation can be easily extended to every classof joints and can work both with straight and curved finite elements simulating links, and with multidimensionalbushings, simulating deformability in joints, . To demonstrate the feasibility and possibleuses, the method has been applied to study the stiffness of the Agile Eye , perhaps the most widelyused spherical parallel robot. Finally, a prototype has been fabricated to make some experimental testsand validations, as shown in Fig. 1.
|Titolo:||Stiffness Analysis of LowerMobility Parallel Robots|
|Data di pubblicazione:||2015|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|