Speed Damping Mechanisms?
Speed Damping Mechanisms?
(OP)
I'm working on a museum exhibit where a 65" plasma monitor (150lb) is manually moved back and forth along a 15' linear rail. We're looking for a passive (non-electronic) means of limiting the speed to thwart kids flinging the screen from one end to the other. We want the screen to move freely at slow speeds but max out at ~0.5 ft/s. I may be wrong but the long 15' run and seems to preclude using a cylinder. Are there stock solutions to this problem? As always, any advice is much appreciated.





RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
Heckler![[americanflag] americanflag](https://www.tipmaster.com/images/americanflag.gif)
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
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"Avoid the base hypocrisy of condemning in one man what you pass over in silence when committed by another." -- Theodore Roosevelt
RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
Hydraulic system
Springs
Leadscrew
Insertia reel no locking reactor (ala, common seat belt)
Attach a hundred helium balloons to the top
Security Guard that wages their finger at the kids
:)
Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group
RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
My concern is that the torque vs. RPM curves for the few rotary dampers I've looked become linear rather than asymptotic (or even quadratic). That is, rather than maxing out the RPM with increased applied force, you can always get them spinning faster. This is a worry where forces range from gentle (an older person pushing gently to move the screen) to extreme (a pack of rambunctious hellions throwing all of their weight into it).
Take, for example, this product from Enidine,
http://www.enidine.com/RVDmain.html#specs
http://www.enidine.com/pdffiles/RVD-Innovation.pdf (curves)
They have relatively-low breakaway torque (3-6 in-lbs) which is nice - means that (ignoring inertia and rail friction), the screen can move with a gentle push. However, even for the most viscous option, 40 in-lbs gives you 500 RPM.
Or am I misunderstanding these engineering curves?
RE: Speed Damping Mechanisms?
Harold
SW2007 SP2.2 OPW2007 SP0.0
www.lumenflow.com
RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
The defining function of a damper is T = f(n), where T is torque and n is shaft rpm.
The faster you try to spin the shaft, the more torque the damper resists with.
Something like this:
http://www.efdyn.com/uploads/379.pdf
would seem appropriate.
RE: Speed Damping Mechanisms?
Yes, I understand this ... but (and I might be wrong) the details of the function f(n) matter. If torque is linearly proportional to rpm, the kids might still be able to get the screen moving at a fair lateral speed. Ideally we'd like f(n) to be be vertical at some relatively low rotation rate
I guess we just spec the damper based on the maximum reasonable force that a person can exert, figure out the corresponding rpm, convert this to a lateral speed (depends on details of the rack and pinion system, and then get damping end stops capable of decelerating the screen.
RE: Speed Damping Mechanisms?
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RE: Speed Damping Mechanisms?
I can envision flinging the panel against the clutch engagement. If the clutch is coupled to "ground" on the other side I think that would be nearly as bad as flinging against a hard stop.
Don't forget that you can add multiple dampers in parallel and the torques would be additive.
RE: Speed Damping Mechanisms?
The power "loss" varies with the cube of the rpm.
No working parts or electrical power required.
Install a power input "pulley" on the same shaft as the fan.
RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
http
RE: Speed Damping Mechanisms?
RE: Speed Damping Mechanisms?
Harold
SW2007 SP2.2 OPW2007 SP0.0
www.lumenflow.com
RE: Speed Damping Mechanisms?
Second, a rack driving a rotary damper is a great idea. I think you won't want to have the damping set too high (as you mentioned) because you'll need kids and older people to be able to move it. Even with low damping, it can absorb energy and slow the panel after a hard shove. However, I understand your worry that a sustained push can get it going at a good rate.
Third, I think the problem here is not just the velocity, it's mostly the harsh impact at the stops. Why not use some springs or shock absorbers at the end of travel? Look into Ace Controls or Enidine.
RE: Speed Damping Mechanisms?
Although there is fringing, most of the magnetic field is contained in the "U" of the magnet rail. Things have to bee pretty close to be affected by the magnetic field.
RE: Speed Damping Mechanisms?
As you point out, a fixed end stop is going to cause a harsh impact (even at our desired max of 0.5 ft/s). We might have to rethink the design - perhaps a motor-positioned screen and a separate slide control. Bumping a separate slider into an end stop wouldn't be an issue. Further, the slide would become a target location for the screen (which can lag at its max velocity). At the end, we could "ease" the screen into position.
Thanks to everyone for the suggestions. This is our first experience in eng-tips - what a great online community.
RE: Speed Damping Mechanisms?
I looked into the magnet track from Parker/Trilogy. It's pretty neat that you can buy long lengths or modular. However, the tracks are expensive. A 48" long pc is $2500-$2700 (210 style) and futnuh would need about 4 of them. Being non-contact, it would never wear out, so I imagine the cost would be justified only if it saw constant usage.
RE: Speed Damping Mechanisms?
KENAT, probably the least qualified checker you'll ever meet...