| Volume 25 Issue 4 - Publication Date: 1 April 2006 |
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| Motion Planning of Multi-Limbed
Robots Subject to Equilibrium Constraints: The Free-Climbing Robot Problem |
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| T. Bretl Department
of Computer Science, Stanford University, Stanford, CA 94305-5447, USA |
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| This paper addresses the problem
of planning the motion of a multilimbed robot in order to “free-climb”
vertical rock surfaces. Freeclimbing only relies on frictional contact with
the surfaces rather than on special fixtures or tools like pitons. It requires
strength, but more importantly it requires deliberate reasoning: not only
must the robot decide how to adjust its posture to reach the next feature
without falling, it must plan an entire sequence of steps, where each one
might have future consequences. In this paper, this process of reasoning
is broken into manageable pieces by decomposing a freeclimbing robot’s
configuration space into manifolds associated with each state of contact
between the robot and its environment. A multistep planning framework is
presented that decides which manifolds to explore by generating a candidate
sequence of hand and foot placements first. A one-step planning algorithm
is then described that explores individual manifolds quickly. This algorithm
extends the probabilistic roadmap approach to better handle the interaction
between static equilibrium and the topology of closed kinematic chains.
It is assumed throughout this paper that a set of potential contact points
has been presurveyed. Validation with real hardware was done with a four-limbed
robot called LEMUR (developed by the Mechanical and Robotic Technologies
Group at NASA–JPL). Using the planner presented in this paper, LEMUR
free-climbed an indoor, near-vertical surface covered with artificial rock
features. |
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| Multimedia Key |
= Video |
 = Data |
= Code |
= Image |
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Extension |
Type |
Description |
| 1 |
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Example
1: The three-limbed robot taking two steps. (6.2 MB) |
| 2 |
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Example
2: The three-limbed robot taking many steps. (23.7 MB) |
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Example
3: LEMUR taking several steps in simulation. (4.7 MB) |
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Example
4: LEMUR changing its posture at fixed holds. (9.0 MB) |
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Example
5: LEMUR taking two steps. (13.3 MB) |
| 6 |
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Example
6 : LEMUR taking many steps. (6.4 MB) |
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