GET A (BETTER) GRIP
For all that Willow Garage contributes to the robotics community,
it's not often that they release new hardware. However, they've
announced a new 3D printed adaptive gripper design for the PR2: the
The cool thing about the Velo 2G is the fact that it can passively
adapt to all sorts of objects. You don't have to do any fancy
programming to get the fingers to grip around an object. The gripper
design itself takes care of that for you. This works on square things,
round things, thin things, irregularly shaped things, and all kinds of other
stuff that robots are likely to find lying around your house.
The Velo 2G is just an alpha prototype for now and it's not for sale,
but given the simple design, single actuator, and 3D printability, we're
hopeful it will not be cost-prohibitive once it is available.
Parallel grippers are effective on a wide range of objects and tasks,
executing fingertip grasps between two perfectly opposing pads.
However, adding the ability to envelop objects greatly increases the
stability of the grasp in many situations. The Velo has two fingers with
two joints each and is tendon-driven. Aiming to reduce the complexity
and potential cost, Willow used a single actuator, resulting in an
underactuated design. The gripper executes fingertip or enveloping
grasps by passively adapting to the shape of the grasped object.
Extension is passive, provided by springs.
The route of the tendons and the magnitude of the extension
forces are optimized to execute both types of grasps, and to passively
transition from one to the other based on the shape of the grasped
object. The forces applied to the target object are also optimized to
result in stable grasps in a large set of possible configurations.
The tendon-driven design allows for a modular implementation
with a tool-less quick-change interface between the kinematic module
(composed of the palm and fingers) and
the actuation module (containing the
motor and the transmission). This
interface allows easy experimentation
with various types of kinematic
components, and also enables easy
replacement of the kinematic module
should it become damaged.
For prototyping this design, Willow
explored multiple emerging 3D printing
technologies. The palm and fingers are
3D printed in nylon using an SLS
process. The actuator module consists
of a single motor attached to a
transmission built around a 3D printed
recirculating ball screw.
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