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

T1.3: Numerical 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 1.3, an in depth analysis, aiming at evaluating the effects of the variable parameters of the plant on the achievable performances of the system, has been carried on, using a simple 1 DOF model for the BE mechanics, spring-damper-mass models for impedances of the human limb and of the environment and a simplified controller, having a virtual damper as desired admittance, a high gain velocity control closed on the motor velocity as primary motion control and no stabilizing contributions.

The analysis evidenced that the specified high values of the human limb stiffness and of the environment mass, combined with the specified low values of environment stiffness and of the human limb mass, produce a shape of the Open Loop Transfer Function (OLTF) that is very critical for the stability of the system. For these combinations of the variable parameters of the plant, the value of the max achievable DC gain of the OLTF, able to guarantee a specified minimal phase margin of 30 degrees, is very low, bringing to poor system performances, in terms of bandwidth and resistance forces, that are not compatible with the applications envisaged for the BE.

The analysis also allowed to conclude that the elements preventing the possibility to increase the value of the OLTF DC gain are the high sensitivity of the OLFT to the human limb stiffness and the presence of significant amplification at the resonance of the mechanical transmission.

Different controllers will be tested in the next period, able to reduce those negative elementes.

In sub-task 2.2, the results achieved for the simple 1DOF case has been extended to general n-DOFs system. This has been possible by making simplifying assumptions that allowed to evaluate the displacement of the ZMP with respect to projection of the center of gravity on the support plane as a linear function of the BE joint angular accelerations, as well as to define an equivalent height of the center of gravity with respect to the support plane that is function of the direction of the BE joint angular accelerations vector and not by its module.

The new collaborative control has been implemented and tested in a simulated environment, using a simplified 12 DOFs model of the BE (arms excluded). The simulation has shown that the new collaborative control works properly also in presence of relatively high operator intended velocities, guaranteeing that the ZMP always falls inside the support polygon.

In sub-task 3.3, the detailed design of the gripper has been continued, producing two successive revisions of the device design.

The first revision have been completed at the end of August 2011, while a second revision have been initiated after an internal technical meeting between PERCRO and TELROBOT, in which several elements for improving the design of the device have been identified and discussed.

At present the design of the new gripper is in the optimization phase, aiming at reducing the weight and the encumbrance of the device to make them comparable with the existing gripper developed by PERCRO.