Re: [Emc-developers] I am new here

[Kent A. R. <kn...@er...>]

On 3/29/2012 9:15 AM, Stuart Stevenson wrote:
> Gentlemen,
>   I have seen this project for over two decades. It WAS the next 
> 'greatest' answer to part production. This 'answer' was initiated in 
> the late 1970's.
> Iges was going to be the main tool to machine parts directly from 
> geometry ie (no programmer). The project driver is 'cost savings'.
> The 'stockholders' ultimate dream is for the design engineer to input 
> the design rules describing the object desired and the machine tool 
> then internally creates the geometry and creates the part.
> For thirty years design engineers have spouted the mantra 'In a couple 
> years NC programmers will no longer be needed'. For the most part the 
> design engineers do not realize once the CAM of CAD/CAM is automated 
> then CAD will be the next automation project.
> Iges is a graphics exchange standard. I was a peripheral player in 
> some of the testing during the late 1980's.
> Surface definition has always been the achilles tendon of the 
> automatic geometry to manufacturing project. Boeing was a driver. 
> Wichita was one of Boeing sites so we saw Iges projects and 
> development AND foibles.
> As computer power increases, surface definition becomes more 
> complex/powerful. This complexity/power resulted in surface integrity 
> problems for the Iges translator. The surface designed in system A, 
> iges translated out of system A and then iges translated into system B 
> was not the exact same surface. Sometimes system B would not be able 
> to describe the surface and a hole would exist in the system B model. 
> It is so bad (within the last ten years with system A being the top 
> aerospace CAD/CAM software) I have seen a surface created in system A, 
> iges translated out of system A and immediately iges translated into 
> system A (same computer, same software) result in two different 
> surfaces. The iges IN/OUT translator was unable to recreate an 
> identical surface.
> This led to STEP, which changed the moniker of the automatic 
> programming project to STEP-NC.
> STEP is better than IGES. STEP has not arrived at perfection, YET.
> There are many parameters to consider during the manufacturing 
> process. We have not arrived at the point of removing the programmer.
> thanks
> Stuart
>
> -
Stuart:

I don't dispute your closing statement nor your theme that successive 
technologies have been promised as "The Answer" since the beginning of 
usage of computers in manufacturing applications. These are correct.

I do feel the need to insert several caveats.

1) Yes, IGES stands for "Initial Graphics Exchange Specification", the 
name of the original NBS/GE/Boeing project that began more than 30 years 
ago. In part, that's because the genesis of the idea came through NCGA 
(National Computer Graphics Association) conferences and in part because 
the very moniker CAD stood for Computer Aided Drafting at that time. 
Never the less, IGES incorporated 3D geometry almost from the get-go. 
Over the years, wireframe, surfaced, and CSG representations were 
perfected. There was never any intent within the IGES Committee or its 
successor, the IGES/PDES Organization to address automated CAM 
programming. There were some DoD-driven projects in that area that chose 
IGES to represent their product definition data.

2) Even within CAD-to-CAD exchange, the use of IGES, like all other data 
exchange representations suffered real world failure until CAD buyers 
started holding the feet of their translator writers to the fire. Even a 
perfect specification means nothing unless the translators implement it 
correctly, and if not correctly, at least in the same way. [NB- this 
translator-vs-specification problem exists in every technical arena, not 
just CAD/CAM. Finite element modeling and analysis programs suffered 
from the same problem as early as the 1960s.]

3) The definition of surfaces is one of the trickiest bits in any CAD 
system. Every aerospace manufacturer maintained a stable of applied 
mathematicians to help deal with their problems in their in-house 
systems and many employed a patchwork quilt of programs to deal with 
different aspects (notably "healing" the intersections of different 
surfaces, such as at the root of an airfoil).

4) Some things were done better in STEP and some perhaps not so much. It 
is still my personal belief is that early successes in information 
interchange using STEP application protocols were as much the result of 
many CAD system vendors basing their translators on the work of only a 
few speciality translator-writing houses plus big bucks being shoveled 
from DoD projects to make the demonstrations happen.

5) STEP-NC is, to the best of my knowledge, not an automated programming 
project either. It is yet another specification of information. In my 
opinion, the nice feature of this project is its extension to 
information about processes and technologies. There still needs to be 
software that generates and acts on the specified information. Time will 
tell how intelligent that software will become.

I know historical expositions are boring but think Santayana oft-quoted 
"those who cannot remember the past are condemned to repeat it." [I 
can't read Spanish so I have to take the word of others that this is 
what he actually wrote.]

Regards,
Kent

Disclaimer: I joined the IGES Committee in the winter of 1983 and became 
the Editor for three releases of IGES beginning with IGES V4.0. I was a 
member of the US PDES (Product Data Exchange Specification) project 
which became the basis of the ISO/STEP activity. I was one of the two 
final-copy editors for the Initial Release of STEP in 1994. You might 
say I have a soft spot in my heart for standardization activity, but as 
I once said in a presentation to an Admiral, I believe in these 
specifications *WARTS AND ALL*. Standards are merely tools in our quiver.