Re: A nomenclature question

A Divendres 04 Juliol 2003 14:27, Herman Bruyninckx va escriure:
[...]
> Okay, there seems to be some misunderstanding :-) The ones I propose
> are outlined above:
> 1. homogeneous transformation matrices for the link-to-link
>    transitions
Ok, I have thought how to do it. It's more or less easy. Howeber there are 
some "details" that are very difficult to solve, I think.

> 2. symbolic representation that describes the kinematic family and
>    the conventions used (positive direction, joint limits,
>    connectivities, etc.)

Ok. You prefere to divide this information. I have worked in a ONE class with 
all this information. 

> 3. for each specific family: an efficient and ad hoc implementation of
>    the internal kinematics API.

I think that this point is something to take care. I'm thinking that you have 
to be able to simulate/operate your 321 robot with classes of the its family 
and with the serial6f genreric family.
...
> > Kleinfunger-Khalil nomenclature that the Travelling Coordinate System. I
...
> I don't like very much these conventions that _impose_ how you have to
> choose reference frames, for the simple reason that people loose too
> much time trying to adhere to the convention. While there is no real
> need for such "systematic" conventions: any choice of frames on the
> links and joints will do, and designers most often have very good
> intuition about where they want their joint axes to lie. 

Reading that, I have remembered that almost ALL the papers that I have read to 
find some nice generic model to solve the inverse kinematic are developed 
using some nomenclature to contruct the formules to work with. 

I agree with you with the idea of the nomenclature as a minimal question. But 
for example. If I would like to implement the Manocha method to solve the 
general kinematic inverse, in all of his-theirs papers he (they) develop the 
formulas using D-H, to conctruct the polinomian, working after with the 
\theta_i. I think that this method is nomenclature dependant, or all least 
the information that I have. To have some nomenclature helps you to develop 
formulas to work, I think. 

I insist that I'm a simple student and I'm sure that there are a lot of people 
here (you the first) that a very high level of kinematics to talk about it 
not me. If you think that this is the correct way, ok, we began to think how 
to implement it. I have only my experience to implement this kind of things 
in my master thesis, that all.

> All the
> conventions (including Kleinfinger-Khalil) work with constructions
> such as the common perpendicular between two axes, etc. I think this
> is not really necessary; it maybe _was_ interesting in the past, when
> being able to use only four numbers instead of 6 or 16 was important,
> which is not so important anymore with modern systems... 

big red light, big red light!!!!!! 
The people is lazy. We are lasy. If I need only 4 number to define one thing I 
will use only 4 not 16. This principly can be aplicable to all the things. 

I don't like to _impose_ anything. I would like to have a library that can 
give to the designers all the freedoom that they need. Howeber I think that 
for practicals reasons you have to arrive at some midle point between 
freedoom and feasible thing. I have the image that a very generic library 
implies a very complex structure inside that take care of ALL the posible 
cases, thats all.

> When efficiency is really important, people have always found efficient ad
> hoc formulas anyway.

I'm not an expert. I'm a simple student. I would like to show you an example.

I construct a industrial robot that I _think_ that is a pure 321 with all the 
intersections, parallel axes, etc. My mathematical model of the robot is 
perfect. I have some nice efficients formulas, etc. 

Howeber, the reality is that I don't have exactly an intersection, or I have 
some error parameters. (I'm reading your notes pag.105, section 7.7) To make 
some nice simulation it would be ok, but to work experimentally with my robot 
I will need some general formulas. So, I think that it's very important to 
have efficent general formulas to work experimentally.

Regards,

Leo


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