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Mechanical work and elastic apparatus

PostPosted: July 16th, 2008, 10:14 pm
by Borelli
I have built an apparatus that is intended to measure external work output. It consists of force transducer connected inline to latex elastic tubing stretch to ~twice it’ resting length (via three pulleys) connected to a linear variable differential transducer (to measure displacement) connect via non-elastic cord (very low strain) to a finger. (see figure attached)

1) Does this system seem like a reasonable method of measuring the external work output of the finger? If not please share your comments.

I wanted to check to see if the force measured at the force transducer was the same on both ends of the pulley system (I was nervous that reduced efficiency of the pulleys would cause a difference in the forces from one end of elastic band to the other end) .

2) Should the force indeed be the same at both ends of the elastic tubing?

3)Is it best to have the force transducer at the opposite end of the system than the finger to get the least amount of force variability.

4) If I include the force due to the mass of the LVDT rod, should the force exerted at the finger be the same as the force measured at the opposite end force transducer?

4) I noticed that when I displace the finger that the first pulley moves an angular distance of approximately 20 degrees but the last pulley (closest to the force transducer) does not move hardly at all. Is this alright or an indication that friction in the pulleys is dissipating the force. It seem to my naïve mind that it is o.k. because the elongation of the latex tubing is dispersed across the entire length of the elastic tubing and therefore the opposite end will move very little.

5) If you have any suggestions on how to best test this system (to ensure it is measuring what I want) or any changes to the design please reply.

Thank you for your help.