In the period of reference (December 2011-January 2012) the following sub-tasks have been continued/initiated, according to the TESBE workplan:

T1.4: Experimental assessment of the selected control approaches

T2.2: Implementation and test of the collaborative control

T3.3: Detailed development of the gripper

In sub-task T1.4 the activity has been focused on the definition of suitable criteria for the optimal dimensioning of the parameters of the new force controller, developed in the previous reporting period.

This is needed, since on the one hand, the parameters of the new controller are dimensioned for a given value of the mass of the handled load that, on the other hand, can vary in a specified range.

Even if the straightforward solution would be that of modifying the parameters at run time (non linear control, using an on line estimation of the handled load), to keep low the complexity of the new controller, it was decided to verify its robustness to the variation of the value of the handled load.

The numerical analysis showed a good robustness of the new controller for whatever value of the handled load, belonging to its specified range of variability, is taken as reference for the dimensioning of the controller.  In particular, the analysis demonstrated that the highest system robustness is achieved when the parameters are dimensioned for the minimal possible value specified for the handled load.

Once closed the analysis of the new controller, the activity has been focused on its extension to the multi-DoF case, firstly defining the general architecture of the controller and then selecting the type and location of the additional sensors (accelerometers) required for its implementation.

In sub-task T2.3, the activity has been focused on the definition of suitable compensations for the three source of errors affecting the evaluation of the position of the BE center of gravity, identified in the previous reporting period.

In particular the parameters of the linear transformation between the measured positions of the motors and the corresponding positions of the BE joints have been experimentally calibrated, while the mechanical backlash in the leg abduction-adduction movements has been compensated with a simple contribution depending on the sign of the developed torque.

Furthermore, the compliance of the mechanical structure of the leg has been compensated introducing equivalent compliances concentrated at the leg joints, whose  best fitting values has been preliminary determined for three distinct circular trajectories of the trunk.

Finally, the updated collaborative control has been preliminary tested on the real device, showing a good capability to prevent the overturning of the system for lateral and longitudinal motions of the trunk.

In sub-task T3.3, an updated version of the gripper design (revision 3) has been defined, aiming at minimizing the overall dimensions and weight of the device. Furthermore all the issues concerning the electronics and the Human Machine Interface have been addressed and integrated into the gripper design.