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Ton Van Den Bogert
12-07-2007, 06:36 AM
I received the following reply from Victor Ng-Thow-Hing at Honda Research
Institute.

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Ton van den Bogert, Biomch-L co-moderator

-----Original Message-----
From: Victor Ng-Thow-Hing [mailto:victorngthowhing@yahoo.com]
Sent: Friday, December 07, 2007 1:19 PM
To: van den Bogert, Ton; BIOMCH-L@NIC.SURFNET.NL
Subject: RE: [BIOMCH-L] Asimo robot gait

Hi Ton,

The short answer is I believe the joint kinematics were chosen to avoid
singularities when computing the Jacobian during footstep planning - hence,
the bent knee.
In particular, the walking requires the solution of an inverse kinematics
problem involving the waist and feet, and because of the lack of degrees of
freedom in the leg, singularities can occur near the straight-knee
configuration. However, there has recently been several straight-leg walking
robots from Waseda university (WABIAN-2) in Tokyo that get around this problem
by adding more degrees of freedom.

There may be other factors, such as the choice of a ZMP-type controller for
balance. ZMP control is somewhat more conservative than the way humans achieve
balance.
Also, the walk controller may be trying to stabilize the upper body center of
gravity, and a more groucho-style, bent-knee gait can facilitate this in the
absence of more degrees of freedom in the waist.

Regards,
Victor.
Honda Research Institute