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  #1  
Old 04-04-2010, 03:25 AM
redrichie redrichie is offline
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Default advice on solenoid type device.

Hello, I am not a mech/elec engineer, rocket scientist or electrician even. I am an artist that is trying to reinvent the wheel, so to speak. If anyone is willing to help I am all ears.
I have constructed a solenoid of sorts. The plunger is a half inch diameter neodymium magnet. It gave me more "push" than a ferrite plunger I found. The plunger has to only move at the most 5 mm and as little as 2mm. The "return" stroke (pull back in) is currently supplied via a stationary neo mag net a the opposite end of the coil. Think spring here. The stationary magnet holds plunger in place until I pulse the coil. The plunger extends and then it is pulled back in via magnetics.
I am trying to vary the pulses from 90Hz to 140Hz. I have tried multiple 555 timer type PWM's but I either cant get them to work or they all seem to overheat (the circuit and the solenoid). The last one melted my breadboard and MOSFET together within a couple minutes. Unfortunately this was best achievement, i was able to get up to 30Hz till it all went up in a puff of smoke.
So can anyone tell me a few things.
First: Can a "solenoid" that is no more than 1.5 inches diameter be continually used as an oscillating piston type device, using a .5in X 1in plunger, for long durations of time. i.e...1 hour or more with brief moments of off time?

second: If it is mechanically possible, is there a circuit that can achieve the desired pulsing that I need. Im not sure of the exact amount of force that I need the solenoid to pulse at. But if I manually pulse a 35V 22uF cap (barney style, I tap the neg leg of the solenoid to one end of the cap rapidly) I can achieve the desired pulse in slow motion. I worry that if I can reach up to 140Hz the plunger will just stay pushed out instead of competing the fully pulled in/pushed out cycle. Im up for trying to build my own circuit , purchasing a micro-controller if need be, or outright purchasing a driver that can handle what I need to do. just need the advice on where to start heading.
Any info is helpful at this time. thanks guys
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Old 04-04-2010, 03:38 AM
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blueroomelectronics blueroomelectronics is offline
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Mind if I ask what this is used in?
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Old 04-04-2010, 03:54 AM
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SgtWookie SgtWookie is offline
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I'm wondering if you actually have to use a solenoid arrangement?

Trying to get a solenoid moving at a 140Hz rate will be challenging, to say the least. I doubt you'll even get close without controlling the solenoid with an H-bridge. The mass of the magnet you're using for a piston will require ever-higher levels of current to accelerate/de-accelerate it as the frequency increases. If it's hitting something hard at one end or the other, it may very well cause the magnet to shatter.

I'm thinking a normal rotary motor with a crankshaft & rod attached would easily be able to accomplish your 140Hz requirement.

If that would be too bulky due to the 90 angle "turn" the force would make, there are pretty small "pancake" stepper motors available that are quite flat.

If even that isn't small enough, you might consider using a rotary motor axially, with a swash plate (wobble plate) on it to achieve the desired in/out motion.
Wiki entry:
http://en.wikipedia.org/wiki/Swashplate
http://en.wikipedia.org/wiki/Swashplate_engine

Swash plates were used for many years in the A/C compressors of GM vehicles.
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Old 04-04-2010, 03:55 AM
redrichie redrichie is offline
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Yeah sorry about that. IT will be used in the implantation of a liquid pigment under the first few layers of a humans skin by way of a needle grouping. Aka..the tattoo. I was just wondering if this method of oscillating a solenoid is practical. As it stands right now the traditional device used for this uses: 2 iron cored coils, a iron or steel armature bar, 2 "springs", a cap, and it forms an analog oscillating electromagnet. Pretty much unchanged since the invention of the doorbell ringer.
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Old 04-04-2010, 03:59 AM
redrichie redrichie is offline
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or Edisons engraving machine
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Old 04-04-2010, 04:05 AM
redrichie redrichie is offline
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The swash plate is currently being used quite successfully. A traditional rotary motor with a cam has a drawback. the peak of the stroke seems to lag there longer than necessary. It doesnt have the fast snap back that Im looking for. A cam and motor are definitely smooth. just not the action im looking for. like I said, trying to reinvent the wheel I feel.
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Old 04-04-2010, 04:27 AM
redrichie redrichie is offline
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So as usual with most things, you mention tattoo and anything else in a sentence and people stop taking you seriously. Sgt Wook thanks for reply..Teufel Hunden. Semper Fi
. Hey I didnt say it wasnt a challenge. I just needed to know if I can do it. And if so where do I start. All my research on the web leaves me feeling pretty blank.
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Originally Posted by redrichie View Post
The swash plate is currently being used quite successfully. A traditional rotary motor with a cam has a drawback. the peak of the stroke seems to lag there longer than necessary. It doesnt have the fast snap back that Im looking for. A cam and motor are definitely smooth. just not the action im looking for. like I said, trying to reinvent the wheel I feel.
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Old 04-04-2010, 04:34 AM
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A dual coil solenoid might be faster.
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Old 04-04-2010, 04:37 AM
redrichie redrichie is offline
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Actually I have thought about this, but again it comes down to the driving circuitry. Really dont know where to start on that one. But Im open to suggestions on where to start looking and reading
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Old 04-04-2010, 04:53 AM
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As I mentioned before, I think that the 0.5" by 1" magnet you're using is going to be tough to get up to the frequency range you're looking at, due to the mass involved. You will likely have to look at using a smaller core.

The way you're using the 2nd magnet to pull the core back is anything but optimal. Seems to me that magnetic force decreases at a rate of the square of the distance. So, when the core is at the furthest point of travel and ready to be pulled back, the magnetic attraction is comparatively weak, so it takes longer to de-accelerate the core than it should. Also, having the two magnets stuck together makes it much more difficult for the solenoid to wrest the two apart.

A better arrangement might be for the 2nd magnet to be a toroidal shape, on the other end of the solenoid, and like poles together - so that the repelling force is at it's greatest when it needs to be.

That, or control a single solenoid with a single magnetic core using an H-bridge, or two solenoid windings.

I don't know if neodymium magnets are affected by constant exposure to what amounts to a degaussing field. However, at some elevated temperatures, the magnet will begin to lose strength.
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