closed loop control of solenoid frequency and stroke [Design]

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From: Joerg on 29 Apr 2010 14:03

J.A. Legris wrote:
> On Apr 29, 1:32 pm, "Bob Eld" <nsmontas...(a)yahoo.com> wrote:
>> "Brandon" <brandon.joseph.mo...(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.
>
> Good advice.
>
> I once had a similar project, and no budget, so I carefully removed
> the cone from a small bass loudspeaker, preserving the suspension and
> the electrical connections, and epoxied a take-off point to the
> circumference of the remaining dome over the voice-coil. Driving it
> open-loop with a D/A and a power op-amp, it worked quite nicely for
> the application, which was to simulate the pecking action of a bird.
> Another advantage of a voice-coil over a solenoid is that it can both
> push and pull.
>

Make sure that the speaker center is ok sans cone. I did this several
times and had one series where the coil started chafing after a while,
obviously the centering wasn't quite stable sans cone and sagged.

The good thing is now you can switch to an MP3 file when the boss ain't
lookin'. Tchk .. tchk .. *BOOM ... tchk .. tchk .. *BOOM* :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

From: Vladimir Vassilevsky on 29 Apr 2010 14:13

From: J.A. Legris on 29 Apr 2010 15:50

On Apr 29, 2:03 pm, Joerg <inva...(a)invalid.invalid> wrote:
> J.A. Legris wrote:
> > On Apr 29, 1:32 pm, "Bob Eld" <nsmontas...(a)yahoo.com> wrote:
> >> "Brandon" <brandon.joseph.mo...(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.
>
> > Good advice.
>
> > I once had a similar project, and no budget, so I carefully removed
> > the cone from a small bass loudspeaker, preserving the suspension and
> > the electrical connections, and epoxied a take-off point to the
> > circumference of the remaining dome over the voice-coil. Driving it
> > open-loop with a D/A and a power op-amp, it worked quite nicely for
> > the application, which was to simulate the pecking action of a bird.
> > Another advantage of a voice-coil over a solenoid is that it can both
> > push and pull.
>
> Make sure that the speaker center is ok sans cone. I did this several
> times and had one series where the coil started chafing after a while,
> obviously the centering wasn't quite stable sans cone and sagged.
>
> The good thing is now you can switch to an MP3 file when the boss ain't
> lookin'. Tchk .. tchk .. *BOOM ... tchk .. tchk .. *BOOM* :-)
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/
>

Now that I think of it, I removed the cone so I could also remove most
of the frame, achieving a more compact unit. If you have the room it
would be better just to leave the cone (and frame) intact.

--
Joe

From: Joerg on 29 Apr 2010 16:01

J.A. Legris wrote:
> On Apr 29, 2:03 pm, Joerg <inva...(a)invalid.invalid> wrote:
>> J.A. Legris wrote:
>>> On Apr 29, 1:32 pm, "Bob Eld" <nsmontas...(a)yahoo.com> wrote:
>>>> "Brandon" <brandon.joseph.mo...(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.
>>> Good advice.
>>> I once had a similar project, and no budget, so I carefully removed
>>> the cone from a small bass loudspeaker, preserving the suspension and
>>> the electrical connections, and epoxied a take-off point to the
>>> circumference of the remaining dome over the voice-coil. Driving it
>>> open-loop with a D/A and a power op-amp, it worked quite nicely for
>>> the application, which was to simulate the pecking action of a bird.
>>> Another advantage of a voice-coil over a solenoid is that it can both
>>> push and pull.
>> Make sure that the speaker center is ok sans cone. I did this several
>> times and had one series where the coil started chafing after a while,
>> obviously the centering wasn't quite stable sans cone and sagged.
>>
>> The good thing is now you can switch to an MP3 file when the boss ain't
>> lookin'. Tchk .. tchk .. *BOOM ... tchk .. tchk .. *BOOM* :-)
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>
> Now that I think of it, I removed the cone so I could also remove most
> of the frame, achieving a more compact unit. If you have the room it
> would be better just to leave the cone (and frame) intact.
>

There is (was?) another option but I am not an audio guy and don't know
if these are still available: In the 70's you could buy coils without
cones. They had a pad attached that you'd screw or glue onto a surface
that you wanted to "insonicate". This way you could turn a divider wall
or other structure into a speaker. The then floating body of the thing
had enough mass to give it a decent sound down to rather low frequencies.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

From: Robert Baer on 29 Apr 2010 18:05

Brandon wrote:
> 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!
One could use an "open" solenoid so that the metal piston can move in
either direction without bumping into an end plate.
That piston ideally would not be magnetically biased so that the
drive would then not need to have a DC offset if uniform mechanical
movement WRT to solenoid is desired. Once working, this is "nice".
Without springs and if centered, this is not going to work too well,
so two solutions: a spring on one end to give mechanical offset (which
then _would_ require DC offset on drive) or magnetically biased piston
which would require DC offset.
For open loop, adjust drive for desired motion.
To close loop, one would need positional sensors (have fun - magnetic
sensors would not exactly be the best).

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