Mark Plecnik, PhD

Discovery and Invention through Computational Mechanical Design

Leg Mechanisms

This page shows an application of the design of six-bar path generating linkages for creating a mechanism that makes a walking motion.  Each six-bar is either a Stephenson I, II, or III type, and they were synthesized in order to guide a point path in a straight trajectory across the ground, then lift off the ground and move forward for another cycle. The example demonstrates how finding near complete solution sets to large degree design equations results in a large number of design choices (in the hundreds).  Linkage animations of some of the algorithm results appears here.

Leg walker design by Mark Plecnik

An embodiment of a leg mechanism for use in a small ambulating robot concept appears below. This embodiment accomplishes the walking motion of six legs in an alternating tripod gait without the use of gears or pulleys. Each leg module is made with compliant joints and motion between leg modules is transferred by compliant pantograph linkages. The robot would be actuated by one motor per side. The compliant linkages would be lasercut, then each side would be attached onto the robot, providing a lightweight, easily manufactured, kinematic system that accomplishes a complex motion with a minimal number of actuators.

A physical prototype of the three legged module from above appears below. The leg module was lasercut from polypropylene in 20 min.

A secondary robot concept appears next. An entire side of the robot (8 leg modules) is made from a single piece. In this case, rotary motion to each leg module is transmitted by pulleys.

This net robot envisions a concept of fabricating a six legged alternating tripod robot from rigid links:

Related to this topic, Festo has recently designed a bionic ant that uses a compliant leg mechanism.

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Dr. Mark Plecnik
Assistant Professor
Dept of Aero & Mechanical Engineering
University of Notre Dame
372 Fitzpatrick Hall
Notre Dame, IN 46556
plecnikmark@nd.edu

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