mechanical structure has been designed considering as basic specifications
the possibility of simultaneous application of the contacts and a limited
complexity of the kinematic architecture, with not more than three controlled
degrees of freedom.
The gripper is shown in a `open'
and in a `close' configuration. Three articulated fingers are present
and contacts with the grasped object can occur along three intersecting
lines equally spaced of 120º. Each articulated finger has a distal phalanx,
that gets in touch with the object, and two intermediate phalanxes, coupled
by means of internal transmissions so that pure translation of the distal
link is generated. In addition to the advantage of using only revolute
pairs, this kinematic structure presents a high ratio between maximum
and minimum extension, obtaining a very large workspace with respect to
the size of the gripper body: the positions of the contacts can range
from a diameter of 3 mm up to 195 mm, being 120 mm the external diameter
of the gripper.
of each finger is provided by a linear actuator, as shown in figure.
The linear actuator is manufactured by Wittenstein Gmbh, Germany,
and is composed of a high-speed brushless motor integrated with a
high-ratio, high efficiency roller-screw mechanism, that allows direct
generation of linear motion
Since the fingers move independently,
the grasping configuration may be any triangle with vertices on the approach
trajectory segments. This feature allows to grasp irregular objects, even
if not positioned in a central configuration with respect to the workspace
of the gripper itself.