My adventures with Auggie.

[tweakie]

I am a little disappointed with the performance of my electromagnet, particularly after Art has spent time at my request increasing the available PRF range of the PWM signal. I was expecting to get up to 80Hz response from my magnet but have found 50Hz to be the limit and even then I have to reduce the travel to 0.5mm which does not give my expected weight to the impact. Reducing the PRF to 40Hz will allow me 1mm of travel and possibly sufficient weight to the impact but the feed-rate needs to be reduced to about 500mm/min., which is painfully slow. Unfortunately everything is a compromise.
In the light of this experience I am going to re-design my electromagnet ? I have a couple of different ideas in mind and it will be interesting to try different designs against each other and hopefully find the optimum.

In the meantime I am back to using the laser and I am just so impressed with the performance of Auggie and all the various effects that can be so easily produced.

Tweakie.

[ArtF]

I have to say thats one of the best photo engravings Ive seen in terms of texture and color
blend. Nicely done.

  Let me know if I can help in the impact area as you go, I have a bit of flexibility in the code
for various things. Id imagine youd need a very fast impact driver to make it work well, Id suggest
a very short stroke.

Ive never done it, but I had an idea once while toying about in another project..

  Youd need a very sharp and hard pointed shaft, in a solenoid with a rubber
hose pressed on the shaft where the point is with the hose extending .2mm
past the sharp point. This would allow the point to drag on the granite or whatever
without scratching it. This also means the shaft only needs to punch .2mm before
impact and needs no return spring as the rubber hose acts as both a limiter and a
return spring. The strength of the hose will limit the speed of travel as its return
strength will dictate the time to retract from a hit.

  As travel time of the shaft will be the main variable in the equation of time
of impact and return, Id think that would allow the max frequency to be much higher.
The frequency Id think would be highly dependent in the inertial moment of the 
shaft and the distance of travel. In testing such a theory here once, (in a very different
context) I used a fuel injector from a car. I could repeatedly do a 1ms stroke time
(and that was in mach3).

    Now if that same solenoid was taken apart,the shaft extended with a carbide
tipped point and held off the stone by .2mm or so
by a hose.. that should allow for 1khz vibration with chips produced.
  I think if the shaft was extended upwards as a place to add small weights one
could tune depth vs hz more easily as the moment of inertia would have a
not insubstantial effect on penetration.

  I could be way off on all of this of course, Ive only played with fuel injector
timing in cnc as a way of making a water curtain..but it occurred to me at the
time that it would have made a fair impact hammer.  I include a picture of
what I was thinking at the time as a time optimized impact hammer. May be
all rubbish though, I don't even know what exactly was inside the injector
as a solenoid.. but I did intend to try it at some point as an experiment..
never got there yet.. its 8,877,846 on my list of interesting things to try.

Art

[tweakie]

Hi Art,

Thank you for your suggestions and assistance (I certainly like the rubber tube idea).
Up until now I have only been able to use Frequency Modulation of the dot pattern (as is used with 1 bit dithered images) and I am reasonably happy with my magnet performance operating in that mode.
However, Auggie has changed everything as it allows Amplitude Modulation of the dot pattern (the duty cycle of the PWM controlling the impact weight of the solenoid and thus the dot diameter). The advantage of this halftone technique being that otherwise 1 bit materials (such as soft brass, chrome, aluminium, etc.) become 8 bit materials and support 8 bit images (without dithering). Roland are probably the market leaders with this impact technology and they use a legacy 8 wire print head from an obsolete dot matrix printer. Although they only use one of the 8 wires their firmware allows selection of another wire when the one in use wears out ? their print head virtually has 8 lives. Not sure I want to go that route but, at this stage, I am considering as many different designs as I can possibly find ? hopefully, something will stand out as being the way to go.

Tweakie.

[ArtF]

Tweakie:

  Interesting.. I wasnt aware of the roland print head thing.. thats kinda funny.. given the cost of
their technology.

Art

[kit]

Gents,
I'm completely ignorant on this kind of technology but can't help thinking that to get something heavy to move that fast it would best be part of a mechanically resonant system which has the 'hammer' continuously oscillating with a gap between it and the actual tool doing the cutting. making a dot then requires a spacer to be pushed into the gap to make the hammer move the tool. This moving spacer and it's associated solenoid could be much lighter than that required to actually punch the tool directly. You might even get really clever and have a wedge shaped spacer to get depth modulation.

Obviously there's an issue with synchronising all the movements and controlling the amplitude of oscillation with and without strikes. Just thinking out loud.

Kit

[ArtF]

That sounds like a reasonable idea.. though maybe a bit complex. It
DOES sound like a good way to modulate a lot of power though.

Art

[tweakie]

Thanks Kit, that sounds like a most interesting idea. It's going to take a lot of thinking about.

Tweakie.

[kit]

I think the only practical form for the resonant hammer is a 'clamped bar' as described in this link. Good luck working out the dimensions for the frequency you want ;D
Somebody else must have had this idea before, there has to be a patent for a working version out there somewhere if you can find it.

Now I really must stop browsing for physics websites and get on with building my upgraded CNC router!

Kit

http://hyperphysics.phy-astr.gsu.edu/hb ... es.html#c2

[tweakie]

Hi Kit,

Thanks for the link - please don?t stop thinking of new ideas, everything helps.

Tweakie.

[tweakie]

This is just a scrap piece of ply which has been painted white. Interesting that this paint has just two tones (plus the base white). Does all white paint have just two (or perhaps 3) tones I wonder ?

Tweakie.