A national project : ANR CoGiRo

The project CoGiRo is a research project which deals with the control of parallel cable-driven robots with and possibly high to very high loads. The overall goal is to propose and validate experimentally methodologies and innovative means to control parallel cable-driven robots with very large workspaces and possibly heavy to very heavy loads. To this end, design and calibration issues will also have to be dealt with. The typical sizes of working ranges considered will vary between around ten meters to a hundred or more meters. For validation purposes, a prototype of a large cable robot will be designed and built.

Project contributions : Calibration of a parallel cable-driven robots

Goals

Improve large parallel cable robots qualities through the identification and certification of a control model.

The complete parallel cable robot model depends on elemental models of the system: cables, mechanical structure, measurement devices and considered mathematical relationships (kinematic, static, dynamic). The first goal is to identify these system parameters. Some of them may be estimated by direct measurement; however, others need to be estimated by a calibration process. One important result is to determine the uncertainties associated with each variable. Indeed, developing a complete model of the entire system is most often not interesting in practice because

• It will be too complicated to use in a real-time controller,
• It will need too many additional sensors,
• All parameters are not interesting for vision based control,
• Certain assumptions are sufficient for specific tasks.

Subsequently, it is necessary to make specific model choices that simplify the controller. These choices depend heavily on a rigorous analysis of the propagation of uncertainties throughout the system. For example, according to the variability and uncertainty in some parameters, some may be neglected whilst others become clearly more important. In this way the mathematical design of the model can be optimally simple for a specific task. Whilst this previous model has focused on online control, it is also necessary to simplify the calibration procedure for the end-user. This may be achieved in a similar adaptive manner, however, additional criteria must be considered. In particular, a decrease in the size and complexity of the calibration procedure.

Partners in CoGiRo:

Dexter (LIRMM), Tecnalia, Rosace (LASMEA)