20 April 2014

MIT MechE deFlorez Competition Entry: Underactuated Robot Gripper

An Open-Source Low-Cost High-Strength Rapid-Prototypeable Underactuated Robot Gripper
by Daniel J. Gonzalez - dgonz@mit.edu
MIT MechE deFlorez Competition Entry
(Hi, Professor Hover!)

 Here is a solid model of my gripper. All of the components can be readily found on McMaster, Trossenrobotics, and other online retailers for under $500.00 total. The parts can be fabricated using only a waterjet, or using online waterjetting services such as bigbluesaw.com. With the solid model released as open-source, just about anyone can put this thing together for use in their robot manipulation project: no expert machining experience required!

The design of this gripper is inspired by the WillowGarage Velo Gripper (Work by Matei Ciocarlie): 

and the design optimization work of Prof. Aaron Dollar of Yale and Prof. Robert Howe of Harvard:

(link to paper: http://biorobotics.harvard.edu/pubs/2010/journal/Dollar_IJRR2010.pdf). 

The design of the drive mechanism is underactuated. Specifically, one motor drives both fingers, each of which has 3 DOFs. Passive compliance between each DOF allows the finger to envelop any given object that fits within its grasp without having to perform complicated grasp planning calculations in realtime. 


As of this writing, the fabrication process is nearly complete, and it should be 100% functional by the middle of next week (~4/23/2014). An Arduino will receive a grasp command from a host computer (or a button for demonstration) and command the servos to either grasp or let go of an object. The Dynamixel servo is torque-controlled and provides torque feedback, so we can apply the proper amount of pressure for a given object.
Here is an example demonstrating the underactuated closing behavior of the gripper that allows for asymmetric grasps. Using constraint tendons, the gripper acts as a standard parallel gripper until the proximal link encounters resistance. The two distal links then close around the object for a snug grasp. 
Here is a cutaway showing the direct-drive spool of the Dynamixel MX64 servo (which can output 7+Nm of torque), the cam lock mechanism actuated by an EMax digital hobby servo, and the main drive cable (Yellow). 

Here is a detailed view of the various active and passive tendons and other components within one of the fingers. Each finger is identical. 

Thank you for considering my project in the MIT MechE deFlorez Competition! 
-Daniel

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