2G "Velo" Gripper

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Overview

At Willow Garage we are constantly engaged in exploration and research work aiming to advance towards future personal robots. In this context, an ongoing project explores novel gripper designs and grasping strategies using them. The Velo 2G Gripper is a result of this exploratory project. Starting from early research prototypes, we have taken the current design to what we refer to as Alpha prototypes, which we are describing here. Based on 3D printing technology, the Alphas can be manufactured in small batches and used for application research and exploration, as well as integration on exploratory mobile manipulation platforms.

Grasping Capabilities

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 can greatly increase the stability of the grasp in many situations. We explored the design space aiming to achieve both of these capabilities.The Velo has two fingers with two joints each, and is tendon-driven. Aiming to reduce the complexity and potential cost, we 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. Passive adaptation also allows the gripper to conform to asymmetric or irregular shapes.

The dimensions of the palm and the links are optimized to execute enveloping grasps on a large set of common household objects. 

   

Quick-change Interface

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. 

   

Construction

For prototyping this gripper design, we 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. The use of 3D printing technologies has allowed us to quickly iterate over design improvements, while still  providing the robustness needed for integration on mobile manipulators and early application research and development.