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

T1.2: Implementation of the selected control approaches

T2.2: Implementation and test of the collaborative control

T3.2: Analysis and preliminary design of the under-actuated gripper mechanism

T3.3: Detailed development of the gripper

 In sub-task 1.2, the unified simulation framework, developed in the previous reporting period, has been tested, verifying the functionalities of all the composing modules.

This tool will be used in the next period to easily carry on a quantitative comparison of the system performances achievable with the different control approaches selected in T1.1.

In sub-task 2.2, the definition of a revised mathematical formulation of the collaborative control has been initiated, taking into account also the effect of the inertial forces on the position of the ZMP.

Through an in depth analysis of a simple 1 DoF system, it has been possible to quantitative define upper and lower limits for both the operator intended velocity and acceleration, ensuring that the ZMP always falls inside the support polygon and that the distortion of the operator intended motion is minimal.

These limits are dependent on the height of the system center of gravity from the support polygon and on the position of its projection on the support polygon.

In the next period the results achieved for the 1DoF system will be extended for a general n-DoF system.

In sub-task 3.2, the preliminary design of the gripper has been completed.

In sub-task 3.3, the detailed design of the gripper has been initiated.

In particular all the components of the mechanical transmission, located between the output of the actuator module and the input of the differential mechanism has been verified/dimensioned, the range of motion of the differential mechanism has been verified in function of the finger postures required to grasp the specified objects and the linkages and springs of the under-actuated fingers have been dimensioned.

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

T1.2: Implementation of the selected control approaches

T2.2: Implementation and test of the collaborative control

T3.2: Analysis and preliminary design of the under-actuated gripper mechanism

In Task 1.2, for the implementation of the different control approaches, it has been decided to develop a unified simulation framework, allowing an easy evaluation of their performances in the scope of predefined range of variability of the parameters, defining the load/environment and human impedances (variability of the plant). The simulation framework is composed by 6 main modules, modeling the BE mechanics, the load/environment and human impedances, the desired BE admittance, the primary motion control law, the stabilizing contributions and one evaluating the performances of the different control approaches according to the method proposed by Hogan.

In sub-task 2.2, simulations carried on a simplified dynamic model of the BE demonstrated that the algorithm defined in T2.1 can effectively guarantee the fulfillment of the system equilibrium conditions only for relatively low velocity of the operator intended motion, while for higher velocity the accelerations produced by the distortion of the user intended motion could displace the zero moment point of the system outside the support polygon. A new more accurate formulation of the control is  now under development, taking into account the inertial forces, previously neglected.

In sub-task 3.2 the preliminary design of the under-actuated gripper mechanism has been continued.

In particular, the differential mechanism, having one input and three output, has been preliminary designed as well as the mechanical transmission from the motor to the input of the differential mechanism.

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

• T 1.1: Review of the existing force control approaches
• T2.1: Mathematical formulation of the collaborative control strategy
• T3.2: Analysis and preliminary design of the under-actuated gripper mechanism

In sub-task 1.1 the continuation of the analysis of the SoA , in the field of control of robots interacting with humans ad unstructured environment, has allowed to identify more detailed methodologies for the system evaluation of the performances and stability of extenders intended for the handling of heavy loads, new control techniques and design methodologies able to guarantee a passive behavior of the interacting robots and new techniques and methodologies applicable to the design and development of motion controller of robots having elastic joints.

In sub-task 2.1 the algorithm and all associated mathematical methods required to implement the strategy for the collaborative control of the Body Extender posture have been defined. In particular the distortion of the vector in the n-dimensional space of the BE DoFs, representing the user intended motion, has been defined in terms of continuous reduction of the norm of the component producing a decrease of the distance of the Zero Moment Point from the support polygon, while leaving the orthogonal component unmodified. The mathematical methods required to find out the direction of projection of the user intended motion has been also defined.

In sub-task 3.2, the link lengths of the mechanism of the three fingers equipping the gripper have been preliminary dimensioned, taking as input the geometry of the objects to be grasped, as specified in sub-task 3.1.  Furthermore a new differential mechanism able to drive the three fingers using only one motor has been conceived to be integrated in the tight mechanics of the gripper. Finally the mechanical transmission from the output axis of the actuator unit to the input link of the differential mechanism has been also defined. All the main mechanical components of the finger and differential mechanisms and of the mechanical transmission have been preliminary dimensioned.

The research activity in the TESBE experiment is organized in three complementary tasks, the first (task 1) devoted to the development of a new fast, accurate and robust force control to be used in a body extender for the tracking of the wearer’s limb motions and for force amplification,  the second (task 2) to the development of a newly conceived  collaborative postural control to prevent the overturning of the system under the action of gravity and iexternal interaction forces, and the third (task 3) to the development of an advanced haptically enhanced gripper able to stably grasp diverse typologies of objects, having different shapes, dimensions and consistencies.

In the first three months of the experiments all these tasks have been initiated according the TESBE work plan.

In particular, in sub-task 1.1 existing force control approaches based on both rigid and elastic mechanical transmission models have been identified, in sub-task 2.1 a preliminary control strategy aiming at preventing the overturning of the system has been formulated in the n-dimensional space of the BE’s DoFs, in sub-task 2.3 preliminary experimental investigation on the efficacy of artificially generated forces at the level the trunk have been carried out and in sub-task 3.1 a preliminary set of specifications for the gripper have been defined.