Hi Yoonsoo,
URDF does not support coupled joints.  Custom transmissions should most
likely be able to do what you have described.
pr2_mechanism_model<http://www.ros.org/wiki/pr2_mechanism_model>has
some examples and documentation on how transmissions are used in PR2.
How are the joint/actuators coupled in your robot?
Thanks,
John

On Tue, Oct 12, 2010 at 11:02 PM, Kim, Yoonsoo <yesarang.kim@gmail.com>wrote:

> Hi,
>
> My robot is composed of various coupled joints for dexterous hands, in
> which M joints are driven by N motors.
>
> I tried to find out how to express coupled joints in URDF but couldn't
> according to URDF XML reference.
> What I only found was PR2-specific <transmission> element. Can this
> <transmission> element express coupled joints and relationship between
> joints and actuators?
>
> If the element can't express coupled joints, any suggestion to do that will
> be appreciated.
>
> TIA
>
> - Yoonsoo
>
>
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