I am looking for a miniature trigger to release a small compression or torsional spring that as about 1 lbf of force at full compression. The trigger should fit in a space about 3X3X3mm or less. I have briefly looked into nitinol wire, voice coils, watch mechanisms, and solenoids, but haven't found anything small enough.
I am interested in any information that may direct me toward existing products or classes of actuators/triggers that may be relevant. Thank you,
Kurt Sutherland
Think of an electrical fuse, without the package containing it. Your spring is held in the compressed state by a tiny length of wire. You apply enough power to vaporize the wire and the spring is released. Running the wire down the center of a coiled spring seems plausible.
Take a look at an "aerotow release mechanisim" as used on full size or model gliders. Might give some ideas. These are designed to release the tow line while it's under tension.
You can get a lot of force when wax melts in a confined space - all sorts of thermostats use this principle, for instance.
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Fuse wire holding back a spring - very compact, very reliable - electrically triggered.
Brian W
Yes like a crude "explosive bolt" these can release massive loads with a very tiny device.
Richard
I had a similar problem a few years ago, had to release a tension spring inside a small area as part of an assembly machine. I designed a mechanism similar to a mechanical archery bowstring release. Visit your local archery or hunting store and take a look at one.
-Dana
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One of the more elegant solutions is to use something made from a "memory metal" alloy. When you run a current through it, it deforms, and when it cools, it goes back to normal.
See
Back in the 1980s, someone at Stanford built a Frisbee which could be shot down with a laser tag gun. It used a shape-memory alloy latch to hold down a fin. When a laser beam hit the sensor, current flowed through the latch, which deformed and released the fin. The fin acted as a speed brake and caused the Frisbee to crash. Neat idea, too expensive back then.
John Nagle
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