consistent number of preliminary experiments has been performed on single
finger modules and sensorial/actuation subsystems in order to test the efficiency
of each finger structure and of the control system. The validation has also
included verification of the procedures for the object approach, based on
the integration of the distance and the position sensor information.
Moreover, a set-up has been prepared in order to perform different experiments using the prototype, where absence of gravity is partially simulated by suspending the objects with a wire. The first experiments include demonstrative tasks of the following procedures:
Concerning the approach and contact phases, it must be observed that the possibility of independently moving the fingers has noticeably increased the capability of grasping moving objects. As a matter of fact, the object may be tracked (if moving) with a coordinated movement of both the arm and the fingers. Once the motion is tracked (i.e. the fingers move syncronously with the object), the grasp may be firmly applied without loosing contact.
As an example of this procedure the positions of the three fingers are shown while approaching a moving object. When the distance from a finger from the object is less than a threshold (5 mm in this case), the position set point is computed in order to remain at that fixed distance from the surface (also if moving) until all the three fingers are in this situation. In the figure, two cases are reported: at the left the approach phase of a almost fixed object, while on the right the track of a moving object (in this case a sphere) within the workspace of the gripper.
In the figure above another test is reported concerning the grasp of a floating object. In this case, the approach motion is stopped until all the three fingers are at the same distance from the object, then the contacts are applied.
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