Oct 3, 2012 , by
In the period of reference (April 2012-May 2012) the following sub-tasks have been completed, according to the TESBE workplan:
T1.4: Experimental assessment of the developed control approaches
T1.5: Validation on elementary handling tasks
T3.4: Validation of the new gripper
In sub-task T1.4, after having implemented multi-DOF force control, as defined in the previous reporting period, it was decided to test its performances for the case of the tracking of the operator foot movements, being more demanding for the large variability of the mechanical impedance of the human leg.
It was assessed firstly the performances of the Feed-Forward (FF) contribution and secondly the improvements achievable adding the Full State (FS) Feedback contribution.
The test showed a good capability of the FF contribution to produce movements of the foot substantially aligned with the interaction force exerted at the foot, demonstrating to have achieved a good decoupling between the different DOFs of the legs.
The adding of the FS contribution has allowed to increase the tracking performances in terms of accuracy and bandwidth, but practical limit exists to the increase of the gains of the FS contribution, due to the non consistency between the variable sensed by the accelerometer (absolute acceleration of the foot) and the variable that can be controlled by the actuators (velocity of the foot relative to the backpack).
In sub-task 1.5, the validation of the controller has been performed evaluating its tracking performances on elementary motion tasks.
In particular three specific tests have been carried on, the first evaluating the tracking performances in case of foot motions, the second in case of hand motions and the third in case of trunk motions.
All the tests showed a significant reduction of the resistance forces achieved by the new controller with respect to those achievable with the original controller of the BE, being in the range of 5÷7 times less.
Being the intensity of these forces well under the target value of 20N in every operating conditions, the movements of the subjects operating the BE resulted faster and more natural than those achievable with the original controller.
In sub-task T3.4, after having integrated the gripper (hardware and software components), a number of validation tests have been performed to assess the effective capability of the device to grasp different object shapes and to make the operator aware of the stability of the force closure.
For the grasping test, cylindrical and conical objects having different dimensions have been used. The device showed an excellent capability to automatic adapt the posture of its fingers to the shape of the objects, exerting grasping forces on the finger contact surfaces and on the palm surface sufficiently high to guarantee stable grasps that could withstand external forces and moments acting on the objects in the range of those exerted by the Body Extender.
Other tests have been performed to assess the suitability of the haptic feedback provided by the device, to make the operator aware of the stability conditions of the grasp. The test demonstrated that the combination of the displacement and force felt by the operator at the trigger of the gripper is sufficient to drive him to the achievement of a stable grasp, having at the same time the possibility to modulate the grasping force.