Re: [CAD_CAM_EDM_DRO] Re: degrees of freedom Was: Angle Iron Ways

Graham Stabler wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephen Wille Padnos
><spadnos@...> wrote:
>
>
>>Hi there.
>>
>>I think that four struts aren't enough, unless you can control the
>>joint angles in addition to the strut length.
>>
>>
>Yes and no. It depends what you call a strut. It you mean an
>idividual rod then you are perfectly correct but you can build your
>struts out of two rods arranged as parallelograms, this gives angle
>contraint. So you always must contrain in 6-axis while moving in the
>number of axes you want to move in. This way it is possible to built
>2-6 axis parallel machines.
>
>check out the diagrams on my page:
>
>http://www.indoor.flyer.co.uk/kinematics.htm
>
>Graham
>
>

Interesting images and machines there!

I like the tilting head in the second photo (the rendered purplish-blue
one).

Of course, constraining the struts from "swaying" also restricts you to
three or four axes of motion on the head (and it does constitute
"controlling the joint angle" ;) ). That one can move "in and out"
linearly, but has no side to side capability. It can tilt in two axes
of course. So you have three struts and three DOF (Z, A, B) -
interesting ;) (In fact, if you fix one of the struts, then you remove
the ability to move in Z, so you get just a tilting head in A,B). Gotta
love mathematics :)

I like that design, it gives me food for thought.
- Steve