Improving the pose accuracy of the Delta robot in machining operations

The main objective of this work is to study the elastic deformations affecting Delta parallel robots during machining operations (e.g., milling). These deformations always induce errors on the programmed tool trajectories. A mathematical evaluation model of these errors has been established. Firstly, this model enables the evaluation of positional errors. Secondly, a compensation procedure of these errors can be performed by instantaneously correcting the motorized joints variables. This procedure is based on the concepts of beam theory involving in particular CASTIGLIANO’s theorem. These deformations (errors) are evaluated at the end effector of the mobile platform. They are estimated as differences between the poses of the end-effector in both hypothesis cases: rigid and flexible. The correction values are obtained by the inverse differential model. The error compensation procedure is performed by an instantaneous correction of the motorized joints variables; the developed approach is applied and exemplified for the Delta parallel robot but remains generalizable to other class of parallel robots.