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12 DOF Control of a Non-rigid Foam Beam

  High DOF control problems involving manipulation of non rigid objects are very hard to solve with traditional model-based robot control paradigms. The modeling of the problem can be messy or completely impractical, which makes design of a control system difficult. Our adaptive controller, on the other hand, does not need an exact a-priori model. Instead the robot learns and refines successive linear models of the complex and non-linear overall visual motor model while performing its task in the real environment.

This experiment uses two 6 DOF PUMA manipulators, one attached to each end of a piece of flexible packing material foam. The attachment is rigid, so the arms can exert torques as well as forces to the beam. The object of the system is to bend or fold the beam into a specified shape. The manipulation is specified by showing the system a sequence of images of the desired manipulation. The Oxford snake trackers [Curwen and Blake, 1992] we usually use for contour tracking rely on an affine constraint. We could not get them to track the foam edges through non-rigid deformations. Instead a point representation of the foam outline is tracked using special purpose trackers on the markers seen in Fig. 5.9gif. From a visual motor model point of view this is a hard problem, in part because the overall model is highly nonlinear. We also start from a nearly singular state (nearly straight beam). It turned out that we needed to show a sequence of at least 3 images during training in order to generate a convergent (sub)goal way point sequence tex2html_wrap_inline4192 .

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Figure 5.9: Carrying out the foam folding task



Martin Jägersand