jim@psitech.com (Jim Rothrock) (11/17/90)
In article <1990Nov11.205704.24949@watmath.waterloo.edu> mwtilden@watmath.waterloo.edu (M.W.Tilden, Hardware) writes: > >...All the kids toys you might >have seen using nitenol use ice as the flex medium. Sub >room-temperature mediums help nitenol keep it's 'memory' but >are very difficult to implement in a robot limb (unless you pump >freon through it, but to what point. If you're going to do all >that plumbing, why not just go hydralic?). How about using Peltier-effect heat pumps to cool/heat the wire? There is a company that markets these as "Frigichips." Run current through them one way, and one side of the chip gets hot and the other gets cold. Reverse the current, and the hot and cold sides exchange. Thus, you would get quite a bit of control over the wire's temperature. The main problem with this technique is that the frigichips are flat and square, from about 1/4"x1/4" to 1"x1". The wires, of course, tend to extend along an entire length of robot arm. The solution I've been thinking of is to have a "clump" of very short Nitinol wires attached to one side of the chip with some sort of heat-conductive glue, and have the other end of the "clump" attached to a reverse block-and-tackle. The block-and-tackle cable would then attach to the next segment of the robot arm. Jim Rothrock | Disclaimer: My opinions do *not* represent the opinions jim@psitech.com | of PsiTech, Inc.
dll@teda.UUCP (Dan Liddell) (11/20/90)
I have seen ohmic heating used as a method of providing the temperature change required by nitinol. You run power through the nitinol itself, it is heated due to resistance, and then you get the phase change that provides the motion you are after. The response was very rapid (for small pieces of metal). I could see where this might not work for large cross sections, or low ambient temperatures. -- Dan Liddell UUCP decwrl!teda!dll TELEPHONE 4089805200 USA curb your dogma. The opinions and views expressed are Dan's.