Vibration Generation advice needed

[GoodVibe]

Ok, call me unbalanced, but I need some advice on generating a vibration at between 60 and 80 hz. I'm thinking an Electromagnetic shaker might be the way to go, but I am open to any and all suggestions.

The key is variable intensity or eccentricity at a fixed frequency. Linear oscillation is preferred, but if there were a reliable way of varying rotational oscillations, I would be very interested.

If the device could generate oscillations/vibrations at different wave patterns, that would also be excellent. The ability to switch between a basic sine wave and something more square edge would be very cool.

A final requirement is size. Ideally, the solution would be able to fit in a cylinder 1" or less in diameter, with the oscillations induced perpendicular to the length of the cylinder.

So, any suggestions?

 

[SomptingGuy]

This thread is getting very interesting. Is the "device" what I think it is?

 

[GoodVibe]

SomptingGuy: Sure is

Qmavam: 10 watts might very well be necessary, but I'm not sure what my test voice coils can handle. I know I can always feed in a very small signal to a 10 watt, but I don't want to get carried away and burn em up.

Battery power would be ideal, but a wall wart is always an option.

As far as displacement, 2mm might very well be too ambitious, and possibly painful at 80hz. Having a smaller displacement is not a very large concern right now, as long as the oscillations are transmitted effeciently to the target area.

My big question now is whether to have an armature driven by the voice coil oscillate directly, or use to device internally to induce oscillations in an external shell. I feel that direct application is probably the most effecient, but I have concerns about the effect that direct mechanical resistence to the movement to the voice coil would have. Any thoughts?

 

[GoodVibe]

BTW, my collarbone is making drawing very very slow. Will have something soon though.

 

[GoodVibe]

Project Update:

Have version .0001 working with a standalone 1 watt amp. Direct application of the oscillation is definitely the way to go. I used the voice coil of a Maxtor 6 gig desktop hard drive to test with. The 1 watt LM386 amp works fairly well, although there are some noise issues. Power will need to be boosted past 5 watts, and will probably end up right at 10 watts. While this doesn't look good for battery life at full power (20 minutes?), I should be able to squeeze 2-3 hours at "normal" power levels with a decent nimh pack.

Just out of curiosity, I hooked it up to my NAD 80 watt. While I doubt my actual output was greater than 5 or 10 watts, I was able to verify that the mechanical power output of the voice coil was more than adequate. Additionally, noise levels are extremely low when it is not hitting the bumpers at the edge of its range of motion, which given the application is a huge benefit.

Estimated frequency response is 1hz to 1000hz, with a range of motion of +5mm at <10 hz to maybe .5mm above 100hz.

If anyone would like to see pictures of the prototype, let me know. It's ugly, but it works.

 

[Qmavam]

Glad to hear you have .0001 working.
Is the hard drive "voice coil" you talk about the head drive mechanism?
I think low noise is an important characteristic to work towards.
I would like to see the pictures of .0001.
I bought a 25 watt stereo amplifier last night at
radio shack for $20.00. I need to modify it for line
level inputs, but the price was right. My plan is to
drive a 12v to 120v transformer with the amplifier, this
will give me 120vac of variable frequency. I will then
use the 120vac of variable frequency to power an existing AC line powered "device" It has some problems such as
the 12v to 120v transformer won't work efficiently at
20hz or 300 hz, but it is a start.

 

[GoodVibe]

Qmavam:

Very interesting.

The voice coil is indeed the drive head mechanism. The roughly triangular shape will force a redesign of the form factor, but it could work out better than the cylinder we were originally thinking of.


BTW, I spent most of yesterday afternoon listening to music by touch with this device. Amazing the detail you can pick up. Gave me some ideas for a future project.

 

[Qmavam]

My thoughts of driving an existing device (120v 60hz)
at different frequencies has been disappointing.
The efficiency is very poor as I move away from 60hz.
Not much vibration anywhere except 60 hz, even though
the voltage remains constant.
I have a solenoid with a 5/8" hole in the center.
If I put magnet in one end and a second with opposite
polarity at the other end I get good response at a wider
frequency range.
Cheers

 

[rorschach]

Goodvibe, Have you looked at the mechanism of Philip's Sonicare toothbrush? Theere may be possibilities there as well.

 

[GoodVibe]

Definite possibilities. Their patent description is very close to the specs on what I was originally thinking.

Problems. They mount the permanent magnets on the oscillating armature. I worry that this might limit the overall power of the device and require (as you can see in the patent drawings) a very large electromagnet. Right now, I am blown away by the power to size ratio of the voice coils, and feel like the sonicare design might be taking a step backwards.

Also, while I have never owned a Sonicare toothbrush, I seem to remember there being "some" noise in the system, which again would be a step backwards from "might as well be silent" with the voice coils. Now, there doesn't appear to be any real reason for noise with the soniccare system, since the armature is isolated from contact with the electromagnet. Perhaps poor quality pivots? Looseparts somewhere inside? Or transformer type hum from that massive electromagnet. Who knows.

Anyway, very interesting idea, and one which I believe would work for the application, but possibly not the way to go.