The Parallel Structures Initiative (PSI) is a prospective work initiated by the Technical Committee on Computational Kinematics of IFtoMM for the study of the kinematics of mechanisms with parallel structure.
Parallel robots have been intensively studied in the last 20 years, mostly in the motion simulator community and in the robotics community. Nowadays they are routinely used for some specific applications but their impact will become larger in the future (for example in the machine-tool industry). Still this young research field has not reached the level of accomplishment that has been obtained for other types of mechanisms such as serial robots.
This can be understood for theoretical problems as the total amount of man/year devoted to the study of parallel structures is still very low while these structures may be considered as the more complex mechanisms.
But even as the most basic levels they are considerable differences between the state of the art in parallel structures and others mechanisms. For example there is still no standard way to define a parallel mechanism similar to the Denavit-Hartenberg parameters used for classical robot.
The purpose of the PSI is to initiate a collaborative work among academics, companies and end-users in the field of kinematics for parallel structures. Three main objectives have been identified:
This standard should allow to define any kinematic structure and to enable one to obtain in an automatic way the kinematics equations of the structure
This simulation tool should take as input a description of the structure as provided in Objective 1 and to output realistic evaluations of what will be the performances of the given structure. For example the simulation tool should be able to determine what will be the worst case accuracy of the robot when it is moving within a given workspace, for given sensor errors. A possible approach to this problem is first to analyze the various types of performance index that may be of interest in order to define a reduced set of well defined mathematical problems called the standard problems set (SPS). For example determining the worst case accuracy of a parallel structure over a given workspace and the maximal joint forces for a given load on the platform are at the mathematical level the same problem, although they are dealing with very different physical entities. As soon as the SPS has been established it will be necessary to develop solving algorithms for each problem in the SPS, that will be incorporated in the SPS Solver (SP2S). If a generic SP2S can be developed, then the performance evaluation of a parallel structure may be performed using the following steps:
This tool should should take as input a description of the structure as provided in Objective 1, in which the dimensional parameters are now unknowns, and a set of design requirements. It will then output for the design parameters either a solution, an approximation of all the solutions or, ideally, all the solutions.
If the above Objectives can be successfully reached, it will then be possible to design efficiently parallel structures of any topology according to the task they will have to performed.
If you intend to contribute to the PSI please send an e-mail to ejck@sophia.inria.fr with PSI in the Subject line and a short description of what can be your contribution to PSI. As soon as a minimal task force has been established we will organize more formally the PSI.