The High Dexterity Underwater Gripper is based on a electrohydraulic actuation technique (the Direct-Electric-Drive Fixed-Volume Closed-Circuit Hydraulic System), proprietary of Eureka Engineering.
A prototype of the High Dexterity Underwater Gripper has been developed by Eureka Engineering as a subcontractor of DIST-UNIGE in the AMADEUS II project (MAST programme)
The AMADEUSII prototype features three two-Degree-Of-Freedom fingers, anyway the technique lends optimally itself to the implementation of simpler (e.g., 3 x 1DOF fingers) or more sophisticated designs.
One the bellows (master) is coupled to the electric drive while the other (slave) is coupled to the device to be operated.
The circuit formed by the two bellows and the connecting line, is completely filled with hydraulic fluid; being this fluid virtually non-compressible, the circuit results not only a closed-circuit but also a fixed-volume one.
Thanks to this, the system shows the following main features:
Thanks to the DEDFVCCHS actuation technique, the gripper shows some special features:
The mechanical interfacing to different robotic arms is easily achieved by the use of a customized mechanical adapter.
A miniaturized underwater video camera
can be housed into the mechanical adapter to provide a close-up
monitoring of the manipulator operation.
The finger is formed of two parts, a fixed part and a moveable one; these parts are joined by a cardan (universal) joint, allowing a 2 degree-of-freedom motion.
The moveable part is, at rest, aligned with the fixed one and, thanks to the joint, is free to move inside a cone having the axis coincident with the axis of the fixed part, the vertex located at the center of the joint and a half-width of about 25 degrees.
The fixed part carries the connectors of the hydraulic lines and is mounted to the palm.
The moveable one carries on its free end, the tip, an elastomer termination. The tip's shape, a rounded-edges pyramid, skewed toward the center of the gripper and topped by a hemisphere, is optimized for the manipulation and grasping of objects having different size and shape; moreover the characteristics of the elastomer help to increase the low-contact-force grasping capability.
The enclosure houses: the pressure-compensating device, the electrohydraulic drive, the position sensor and an electrical board carrying the cabling interconnection terminals.
The pressure-compensating device is formed by a flexible bellows mounted liquid-tight to the inner side of the end plate.
The electrohydraulic drive is formed by the master bellows, the linear electric motor and the position sensor.
The linear electric motor is of the voice coil type, more specifically is of the moving-coil type; that is, the motor stator houses the permanent magnets and forms the magnetic circuit, while the coil moves inside the gap of the circuit.
The master bellows and the linear motor are placed on the same axis, and the moveable end of the bellows is directly coupled to the coil assembly, so friction and backlash phemomena are avoided.
A miniature LVDT (Linear Variable Differential Transformer) linear position sensor is used to accurately measure the motion of the moveable end of the bellows.
The cage is provided with handles for transportation, and makes it easy to mount and fasten the assembly on board of an underwater vehicle.
The hydraulic lines bundle, 3m in
length, allows the installation of the gripper on many of the currently
available underwater robotic arms.
Power requirements: 24 VDC, 30 A
gripper: 250 (l) x 200 mm (dia) [approx.]
electrohydraulic drives assembly: 500 x 380 x 450 mm [approx]
Weight: 35 kg [approx]
Full text of Patent (.pdf, 85kB)
Here are some gripper's movies
DIST1 (.avi, 1.6MB)
DIST2 (.avi, 8MB)
DIST3 (.avi, 8MB)
DIST4 (.avi, 8.6MB)
DIST5 (.avi, 8MB)
EGG (.avi, 4.5MB)