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From: Michael A. Terrell on 29 Apr 2010 18:49

"J.A. Legris" wrote:
>
> I once had a similar project, and no budget, so I carefully removed
> the cone from a small bass loudspeaker, preserving the suspension


The suspension is called a 'spider'.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
From: Robert Baer on 29 Apr 2010 23:28
Michael A. Terrell wrote:
> "J.A. Legris" wrote:
>> I once had a similar project, and no budget, so I carefully removed
>> the cone from a small bass loudspeaker, preserving the suspension
>
>
> The suspension is called a 'spider'.
>
>
Is it found somewhere tangling with the web?
From: Michael A. Terrell on 29 Apr 2010 23:44

Robert Baer wrote:
>
> Michael A. Terrell wrote:
> > "J.A. Legris" wrote:
> >> I once had a similar project, and no budget, so I carefully removed
> >> the cone from a small bass loudspeaker, preserving the suspension
> >
> >
> > The suspension is called a 'spider'.
> >
> >
> Is it found somewhere tangling with the web?


No. Early speakers used a very crude suspension that looked like a
spider web. The speakers were so crude that there were adjustments to
center the voice coil.

Later speakers were made of stiff fabric that were glued to the frame
& the cone so the alignment didn't change, as long as the cone wasn't
damaged.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
From: Tim Wescott on 30 Apr 2010 01:53
Bob Eld wrote:
> "Brandon" <brandon.joseph.moore(a)gmail.com> wrote in message
> news:7de228e2-e708-4a28-a1d6-119b74aaf5c6(a)s2g2000yqa.googlegroups.com...
>> I have a project in which I would like to produce a "smooth"
>> reciprocating motion with an adjustable stroke length between about 1
>> mm and 2 mm and an adjustable frequency between 100 Hz and 150 Hz. I
>> think there might be some advantages to using a solenoid for this (as
>> opposed to a rotary motor and a mechanical design) but only if I can
>> get good feedback control of the stroke and frequency. In a spring-
>> mass mass system frequency can be controlled open-loop, but I'm not
>> sure how well I could regulate the end and start position of each
>> stroke or even what sort of sensor might be appropriate and have a
>> fast enough response and a clean enough signal to work at that
>> frequency. Wondering if anyone has any good electronic (or
>> mechatronic) ideas as to how this might be done.
>>
>> Thanks!
>
> What does "smooth" mean? A solenoid is one way but they are non-linear and
> may be difficult to control the stroke length because of inertia etc. How
> much force do you need and what is the precision of motion and position
> necessary? The best way for precision motion, controlled velocity and
> position is a voice coil actuator. These can be designed with any force from
> few dynes up to tonnes if necessary. The feedback can be acceleration,
> velocity or position with various sensors, accelerometers, coils, linear
> pots or line encoders. There are many options depending on what you are
> trying to do.
>
> Voice coils have the advantage over moving iron devices like solenoids of
> having low mass and a linear current to force function which makes them much
> easier to control. They have much wider band width as well. More information
> would be helpful.
>
>
More information would be really helpful. And I second the thought that
a voice coil would be better than a solenoid, unless you have strong
reasons to want one.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: Brandon on 30 Apr 2010 11:38
Thanks for the responses. Lots to think about. I have a controls
background, but most of my work has been on the algorithmic/academic
end of the spectrum so I don't really know much about technology
unfortunately.

I guess I can share a few more specifics about what I'd like to
accomplish. It's a hand tool for an artist friend, but it has a
potentially niche-sized market if it's an decent improvement over what
he's using now, so I'm thinking in terms of production.

Minimum requirements:
1) Pretty good frequency control. Any oscillation not noticeable to
the user.
2) Very precise control of one end point of the stroke and reasonable
control on the other end.
3) Little if any noticeable off-axis vibration.

Really nice things to have that would be probably be necessary for
commercial success:
A) Low enough power drain to operate off a small battery (3 cm^3
max???) for a decent about of time. Sorry, I don't have more
specifics on that yet.
B) Production costs for accuator/sensor/electronics of $200 at the
very most. Probably needs to be less than that unless this turns out
to be so great that people are willing to pay substantially more than
the current technology costs.

Other things that would be cool but aren't absolutely necessary:
a) Shaping of end effector trajectory. Lower velocity on out stroke
then on return stroke.
b) Quick adjustment of stroke length.

Force requirements: Pretty small I think. The reciprocating tool is
very light, on the order of a couple paper clips maybe and it doesn't
have to apply much force to the material you're working on. Force
requirements are probably dominated by the friction needed to hold the
tool in place.

That's all I can think of right now.

(2) and (a) make me want to use a cam. The potential problems I see
with this are that cutting an arbitrary cam profile on something small
is not that easy, so (a) may not be that achievable. Expense is also
an issue. Small motors are pricey and even a 16 line encoder that
small seems to cost as much as the motor. Easily over $100 each total
right there which is pushing the limits of what this thing can cost.
Accuracy and settling time of speed control is not going to be as good
as I would have hoped for, but it's probably acceptable. Power
drain? I don't know if a solenoid would be any better, but that voice
coil has me intrigued. (1), (3), (a), (b), and maybe (B) and (A) are
what got me thinking about a solenoid, provided that (2) could be
achieved via some combination of physical mechanism and feedback
control.
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