Vibration Generation advice needed
Vibration Generation advice needed
(OP)
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?
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?





RE: Vibration Generation advice needed
You haven't specified what force magnitude you need.
Incidentally, because you have failed to specify so many things I can satisfy your spec with a 3V DC electric motor out of a toy.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Vibration Generation advice needed
We're a little unsure on the exact force magnitude. In general, with a variable force of displacement device, we would look for a displacement of around 1-2mm, which would give a acceleration (rms in g's) of 5-10 at 60hz, or .13 to .26 m/s velocity rms).
The small dc motor toy shakers work except for one thing, the force is locked to the rotational speed. We want to be able to vary the force/displacement at the same rpm or hz. That's the tricky part.
Is there any other detail I can provide?
RE: Vibration Generation advice needed
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Vibration Generation advice needed
I think somewhere in the range of .1 to .5 newtons would do the trick, if that is possible.
Sorry about that.
RE: Vibration Generation advice needed
Have a look at the small B&K acclerometer calibrator.
http://www.bksv.com/pdf/BP0184.pdf
It will shake a 70g accelerometer at 1g, so that is 0.7N
It is a little larger than you specified, but the electrical and magnetic circuit is about right to give you some ideas.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Vibration Generation advice needed
Hmmmmmm....
RE: Vibration Generation advice needed
Your 1" OD restricts you to a fairly small magnet and coil.
designing an idiot proof suspension is the hard part.
Most small shakers are voice coils, in fact I've only ever used a couple that weren't.
What are you trying to shake?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Vibration Generation advice needed
Voice coil is looking better and better. The 1" limitation does make things tricky, but the nature of the product dictates it. I wasn't sure whether to mention the application given the forum, but what the heck. The application is adult in nature and female oriented (if that's to obscure, message me and I'll send you some more details). When analyzing the products on the market, the primary source of vibration is an unbalanced dc motor. The problem with such devices is that the frequency of the female response is very narrow, (between 60 and 80 hz if you haven't guessed) but individual preference dictates variable power. 99% of the devices do this by increasing RPM, usually right past the 80hz sweet spot. The one device that has a solution to the problem is an oscillating electric toothbrush like device that is extremely (and I emphasize extremely) effective.
There are many other engineering challenges, such as battery life, waterproof container, durability, etc... but the big one is variable power at a fixed hz.
I guess it is up to the reader whether this problem is as sexy as a camshaft, but it sure keeps me up nights.
RE: Vibration Generation advice needed
What do mobile phones use as vibrating alerts? I'm guessing unbalanced motors. They must be tiny, so you could just have 4 (or whatever gradation of force level is required) of them, phase locked somehow.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Vibration Generation advice needed
If I had an accelerometer handy, the target surface vibration would be very easy to measure. Maybe it's ebay time.
RE: Vibration Generation advice needed
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Vibration Generation advice needed
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RE: Vibration Generation advice needed
Testing the competition has been interesting. Only one has actually caught on fire, but a few have started smoking.
On the original subject though, it looks like a voice coil might be the way to go. I'll be pulling apart a few hard drives to do some experimenting. The acceleration and frequency response on those puppies are pretty impressive, and might even be worth rethinking the form factor.
Also, if your wives or girlfriends ever give you any funny looks when you're trying something new in the bedroom, just tell them you are attempting to hit 80hz.
RE: Vibration Generation advice needed
I have a low wattage audio amp for power and a variable
oscillator to drive the coil. I need a higher wattage amp and more turns on the coil.
Anyway, I'm interested in your research!
RE: Vibration Generation advice needed
Please forgive my short sentences, broken collarbone (and no, not from product testing)
The 60-80 hz sweet spot has been verified in several university studies and is pretty well known in the industry.
We absolutely want variable frequency with power though, as i suspect each user will vary, some quite a bit. I also wonder if there are biological harmonics that can be tapped in to.
25 to 300 hz would be a minimum range to shoot for. If it can handle the heat, I will shoot for 5=500. Wave shape has been the big breakthrough. I plan on building a 1-5 watt audio amp and driving it with standard audio circuitry and inputs. Think ipod jack. That allows all sorts of interesting complex waveforms. Maybe a high power 10hz combined with a low power 80hz wave?
As far as form, the voice coils I pulled this week from hard drives are looking very interesting. I have a form worked out that is non-cylindrical but a contoured triangle. Will work up some drawings as soon as I figure out how to draw with my left hand. The bobbin arrangement you described is also a very strong possibility. My concerns are heat, and whither mechanical dampening would need to be used.
RE: Vibration Generation advice needed
RE: Vibration Generation advice needed
RE: Vibration Generation advice needed
amp*(2*pi*f)2=max g-level for sinusoidal vibration.
An amplitude of 2 mm at 60 Hz requires 29 g acceleration, conversely, a 10-g acceleration at 60 Hz will only produce a 0.7 mm displacement.
Your stated velocity targets are more in line 10-g acceleration, since amp*2*pi*f = 0.26 m/s with f=60 Hz and amp=0.7 mm
TTFN
RE: Vibration Generation advice needed
effect they would have. My reasoning is, the coil (inductor) is trying to smooth the waveform that you apply and the mass you are moving will be slow to respond to force and continue movement when force is removed.
You mentioned a 1 to 5 watt amplifier, I suggest starting
a little larger, maybe 10 watts. You can always downsize
if you find you don't need the power.
Are you shooting for battery power? Might need to look for an efficient amplifier later.
I would like to see ideas in drawings.
RE: Vibration Generation advice needed
RE: Vibration Generation advice needed
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?
RE: Vibration Generation advice needed
RE: Vibration Generation advice needed
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.
RE: Vibration Generation advice needed
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.
RE: Vibration Generation advice needed
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.
RE: Vibration Generation advice needed
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
RE: Vibration Generation advice needed
RE: Vibration Generation advice needed
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.