Exercise pulley machine for MRI
Exercise pulley machine for MRI
(OP)
Hi everyone, I am building a calf exercise machine for MRI. I have attached a sequence of 3 pictures showing what I have so far with the foot plate (where the patient will rest their foot) in 3 different position. As it is shown, the patient will be lying with the head to the left and their foot will rest in the left part of the machine. They will perform dorsiflexion and plantar flexion (rotating their foot forward and backward) and pushing or pulling against the footplate.
I have it setup so that the force on the footplate is translated to the disc at the right via a lever arm. The goal is to have the same rotation at the angle on the disc which is attached to a weight stack, much like at a gym machine. It's important that their be a linear translation of force from the foot to the weight stack.
Do I have the setup right? Do the radii of the footplate/ankle rotation and disc just have to be the same? You can see that the range of motion is limited with this design which is fine since patients can't rotate their feet too far in either direction, but as you reach the limits you can see that their does not seem to be a linear translation of distance rotated from the footplate to the disc. I've played with a lot of configurations with the axis of rotations for the disc and footplate at different levels and so on. Am I doing something wrong?
Thanks a lot.
I have it setup so that the force on the footplate is translated to the disc at the right via a lever arm. The goal is to have the same rotation at the angle on the disc which is attached to a weight stack, much like at a gym machine. It's important that their be a linear translation of force from the foot to the weight stack.
Do I have the setup right? Do the radii of the footplate/ankle rotation and disc just have to be the same? You can see that the range of motion is limited with this design which is fine since patients can't rotate their feet too far in either direction, but as you reach the limits you can see that their does not seem to be a linear translation of distance rotated from the footplate to the disc. I've played with a lot of configurations with the axis of rotations for the disc and footplate at different levels and so on. Am I doing something wrong?
Thanks a lot.





RE: Exercise pulley machine for MRI
Keith Cress
kcress - http://www.flaminsystems.com
RE: Exercise pulley machine for MRI
RE: Exercise pulley machine for MRI
RE: Exercise pulley machine for MRI
I want the force from the foot transferred to through the rod to the disc/wheel to the right to then pickup the weight stack directly underneath it. So as the footplate turns the wheel, the wheel then lifts the weights stacked below.
I want to make sure that whatever distance the footplate moves or circle it inscribes is the same distance the wheel moves to pick up the weights.
However, it seems that as you reach certain position while turning the wheel, there is no long a linear relationship between how much the foot plate turns and the turning of the wheel.
Thanks for looking everyone.
RE: Exercise pulley machine for MRI
Short strokes and long moment arms help. I'm guessing your setup as is (if the picture is scaled right) would produce less then 20% error (maybe even a lot less).
RE: Exercise pulley machine for MRI
You might be able to negate that a bit by how you attached the output weights to the wheel (a link vs. a cable around the OD of the wheel). You could also mount the link so that it is horizontal at mid-stroke and connected to the top (or bottom) of the wheel (force in link and moment arm at 90 degrees) instead of 45 degrees below the horizontal as shown in the middle picture.
RE: Exercise pulley machine for MRI
Thanks again
RE: Exercise pulley machine for MRI
You said "metals such as brass and aluminum are not magnetized in the field so those are possibilities too"
I'm not certain about brass, but significant eddy currents can be generated in aluminium near large magnetic fields so rather than being "sucked in" it could be levitated and propelled with some force! In fact this is the principle behind Maglev Trains.
RE: Exercise pulley machine for MRI
The metals will not be going into the magnet but used at most in the weight system. Thanks for pointing that out.
RE: Exercise pulley machine for MRI
I had the opportunity a while back to play with an approx 10 cm diameter piece of aluminium plate in a relatively small (1 Tesla) MRI. Moving it up/down or left/right was easy enough. Trying to twist it was like it was submerged in molasses - and the faster you turn it, the more solid it gets.
M
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Dr Michael F Platten