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- Posted on
Looking for a certain transducer
- 04-28-2005
Csaba posted on April 28, 2005, 10:28 am
Usually I give a more specific title to my posts, but the problem is I
don't even know the name of what I'm looking for. So I'm going to have
to describe it...
Summary: I am looking for a small device which can "quickly" move a
weight (about 1/4 kg) back and forth along a short distance (about 3 to
5 cm).
Imagine that you have a steel rod hanging from a ceiling. It's not a
very big rod, only about 18cm (7") long and at most twice as thick as
that part that contains the ink in ball point pens. At the other end
of this rod (pendulum) is a weight (about 1/4 kilo) that can slide up
down the rod, only I want to anchor this weight to behave as follows:
When the rod moves through the vertical position (ie. vertical from the
ceiling), the weight should move closer to the ceiling by about 3 to 5
cm. When the rod has reached a high point in its path (and is
therefore no longer in motion), the weight should retract to its
starting position (see diagram, below).
The question is where can I find (and how is it even called) a device
that will be able to move the weight as I described? The exact times
when the weight movements happen may vary (ie. I am not concerned
about the measurement portion of this problem. We can assume that
there is a signal to the transducer that says 'extend' or 'retract'.
But (1) the rising should be "quick" even though it may be acting
against up to 5g (due strictly to the swinging) (2) the weight has to
be able to maintain that 'risen' position until it gets the signal to
retract (3) the retraction is never against more than 1g (if you
imagine that the pendulum can rise above the level of the ceiling).
Apologies if I have not adequately described what I am looking for. In
that case, please ask for clarification and I will provide it.
Thanks for any tips,
Csaba Gabor from Vienna
Ceiling
|
|
|
|
|
weight (rises as it swings through)
|
|
-
Ceiling
\
\
\
\
\
\
\
weight (retracts to end at high point)
-
don't even know the name of what I'm looking for. So I'm going to have
to describe it...
Summary: I am looking for a small device which can "quickly" move a
weight (about 1/4 kg) back and forth along a short distance (about 3 to
5 cm).
Imagine that you have a steel rod hanging from a ceiling. It's not a
very big rod, only about 18cm (7") long and at most twice as thick as
that part that contains the ink in ball point pens. At the other end
of this rod (pendulum) is a weight (about 1/4 kilo) that can slide up
down the rod, only I want to anchor this weight to behave as follows:
When the rod moves through the vertical position (ie. vertical from the
ceiling), the weight should move closer to the ceiling by about 3 to 5
cm. When the rod has reached a high point in its path (and is
therefore no longer in motion), the weight should retract to its
starting position (see diagram, below).
The question is where can I find (and how is it even called) a device
that will be able to move the weight as I described? The exact times
when the weight movements happen may vary (ie. I am not concerned
about the measurement portion of this problem. We can assume that
there is a signal to the transducer that says 'extend' or 'retract'.
But (1) the rising should be "quick" even though it may be acting
against up to 5g (due strictly to the swinging) (2) the weight has to
be able to maintain that 'risen' position until it gets the signal to
retract (3) the retraction is never against more than 1g (if you
imagine that the pendulum can rise above the level of the ceiling).
Apologies if I have not adequately described what I am looking for. In
that case, please ask for clarification and I will provide it.
Thanks for any tips,
Csaba Gabor from Vienna
Ceiling
|
|
|
|
|
weight (rises as it swings through)
|
|
-
Ceiling
\
\
\
\
\
\
\
weight (retracts to end at high point)
-
Mike Yarwood posted on
Re: Looking for a certain transducer
Hi!
If you are permitted a disc at the high point and a smaller retaining disc
at the low point then you could do it with an electromagnet in the high
point disc and make your 1/4 kilo weight a permanent magnet with a hole
through the middle ?
Best of Luck - Mike
Re: Looking for a certain transducer
Since I'm the one making this thing, I'm permitted to have those
discs, and I'm open to your idea. If I understand you right, when I
want to make the weight extend (move towards the ceiling), then I
should pass a current through a wrapped wire to the high point disc
which will create a temporary magnet, attracting the half pound weight
(permanent magnet) over the 3cm distance. When I want it to go back to
its original position (at the end of the rod), I could just reverse the
current.
Perhaps more importantly, what is/are the term(s) I should search
under to find this type of item for purchase (and I'm happy to receive
the name/site of specific recommended stores - don't worry, I'll do my
homework before purchase). At this point, I just want to experiment
around to come up with proof of concept model.
Thanks,
Csaba
Ned Simmons posted on
Re: Looking for a certain transducer
@g14g2000cwa.googlegroups.com>, Csaba@z6.com says...
I'd start by Googling "voice coil actuator". If you find
you need longer strokes or higher forces than you can get
with this type of device, search on "linear motor" or
"linear servo motor".
I'm assuming you need smooth, controlled motion between the
two end positions. If not, the problem is much simpler.
Can we also assume the actuator must swing with the
pendulum, or might it be possible to transfer forces
through the pendulum's hinge?
Ned Simmons
MetalHead posted on
Re: Looking for a certain transducer
I think that you could do what you are describing with a solenoid.
Pinball machines used them extensively for for actuating the flippers
and bumpers and such. A solenoid has a steel or iron plunger inside a
short tube with magnet wire wrapped around the outside of the tube. If
the plunger is not all the way into the tube when power is applied to
the magnet, it will be pulled until it is. It has been many years since
I have designed a mechanism with a solenoid in it, so I have forgotten
the amount of force availible from them, but as I remember, it can be
pretty substantial.
To make your mechanism work, I would get a steel rod that is the correct
diameter to go into the solenoid and tap the end of it to take a machine
screw. Use a nylon or aluminum (non-magnetic) bolt threaded into the end
of your steel rod to support the rod at it's longest extension. I am
guessing that the steel rod will need to be about 1/3 of the way into
the solenoid tube at rest.
_____
/ \
------------- -------
^ | |
| | |
Solenoid | | Nylon or aluminum Bolt
length | |
| ---
| | |
------------- | |
| |
| |
| | Steel Rod
| |
| |
| |
--------
| |
| | Weight
| |
--------
Next, make a pivoted mounting bracket for the solenoid so that it can
pivot back and forth with the swinging weight below it.
Bob
Mitch Berkson posted on
Re: Looking for a certain transducer
"The Amateur Scientist: How to Make a Pendulum That Will Demonstrate the
Rotation of the Earth" by C.L. Stong from Scientific American pp 115-124,
June, 1958.
It would probably be worthwhile for you to take a look at that and see how
they did it. Although it may not be a requirement for your project, an
interesting aspect of what they did was the consideration that the mechanism
which kept the pendulum swinging not have any directional preference.
Mitch
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