Re: Higher performance systems

Les,

I'm enjoying this thread.

Just a little side note here.....

A friend has a large machine designed for mold making. It uses one
of the newer Fanuc controls designed for high speed contouring. He
doesn't program in feedrates, but in accuracy. By accuracy I mean
he tells the control how close the actual toolpath must be to the
programmed path and lets the machine self determine it's feedrate
based on the part contours. I believe it's just a matter of
selecting one of the pre-determined accuracy settings in the control.

Regarding the issue of high performance.....

In my experience for general metal machining it's more important to
have a high rapid rate then it is to have high speed contouring
capibility. The cutting rate is usually limited by tool/material
issues while the rapiding between cutting locations doesn't have
those constraints and is usually a straight path.

A question....

Is this work on high speed contouring just an academic exercise?
Plenty of commercial machines are on the market that will do this
already. Buy the commercial machine and start making parts tomorrow
and you'll spill more money on the way to the bank than the DIY
builder will ever make with his machine. The last statement is a
slight exaggeration, but in my business experience that's what I've
concluded.

thanks,

Doug




--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Leslie M. Watts"
<leswatts@a...> wrote:

> Mariss,
>
> The topic is near and dear to me as well as we are quite
> hard at work trying to implement FUNCTIONAL third order
> splining in the EMC trajectory planner.
>
> And yes I would describe the math as "a little busy"!
>
> I will get to your group and read about your system.
> If it is all digital that moving average must be
> a rectangular convolution that might be done with
> an FIR digital filter with constant coefficients-
> otherwise known as a nested loop.
>
> Your method must go beyond the second order (arc, parabola,
> or ellipse) rounding that automatically happens when
> acceleration (torque) is limited to a particular value as
> it of course always is.
>
> Integrating velocity over a finite (moving)interval would seem
> to make accel dV/dt tend to look more like the original
> unfiltered V(t) since it would be the integral of a derivative.
>
> Anyway, interesting. I will follow up on your group to
> avoid too much math gibberish here.
>
> A note also for Josh... Doing 3-d contouring can be very machine

time

> intensive so yes routers and such typically can have quite high
> feed rates and correspondingly high accelerations so corners can be
> sharp at speed. In the big machines cutting at several FEET per

second

> is common.
>
> But to use those speeds you have to have a LOT of spindle

horsepower at

> high rpms. Many of those fast machines have 25 HP+. If you are

using

> a small router motor you may not need such high travel speeds

simply because

> you can't push that router through the work that fast. An

exception might be

> cutting foam or something that requires little power.
>
> High rapid speeds might not be such a big issue either if your code
> is not cutting a lot of air.
>
> You might try some manual speed/feed tests to see how fast you can

really

> go with the spindle you use. If you can go a lot faster than your
> current stepper tables then it would justify something with higher
> performance.
>
> Very high speeds and accelerations tend to be very expensive

though!

>
> Les
>
> Leslie M.Watts
> L M Watts Furniture
> Tiger Georgia USA
> http://home.alltel.net/leswatts/wf.html
> Engineering page:
> http://home.alltel.net/leswatts/shop.html
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>
>
>
>
> -----Original Message-----
> From: Mariss Freimanis [mailto:mariss92705@y...]
> Sent: Thursday, August 28, 2003 7:25 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Re: Higher performance systems
>
>
> Leslie,
>
> Ah, a topic near and dear to me just right now! The conundrum is
> vector path fidelity and a constant vector velocity are mutually
> exclusive.
>
> To accurately follow a path means you have to decelerate to a stop

at

> the end of every line segment which is irritatingly slow and noisy.
>
> You can "round" line segment nodes to keep a constant contouring
> velocity. It is a computational nightmare though, having to insert
> arcs between nodes whose start and end angles and radii depend on a
> given axis set acceleration and velocity. The "on the fly"
> trignometry and path look-ahead schemes get real ugly real fast.
>
> I have come up with a method that neatly sidesteps those problems
> entirely; it is computationally trivial and acts automatically. In
> effect, the faster you go, the "rounder" the nodes are.
>
> The method outputs a moving average of velocity, effectively
> integrating velocity with time. A step change in velocity gives a
> ramped change, a ramped velocity results in an S-shaped velocity
> profile.
>
> As you probably know the G2002 is up and running using this
> algorithm, now on 3-D moves (XYZ). The results are very pretty

indeed.

>
> Mariss