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Richard Erlacher
09/15/12 09:59
Read: 606 times
Denver, Co
USA


 
#188339 - I don't follow ...
Responding to: Jim Granville's previous message
I'm not sure what you mean with your "U" and "O" tracks, but I'd point out that the limitation on precision is imposed by the size of the probes. The size is limited by the fact that accidents could cause injury if the probes are very small, even if the pressure is quite limited.

Optical means can measure surface contours under zero pressure quite accurately, but don't do so well once some deflection occurs.

It's quite important to know not only where the hard areas are, but also how soft the soft areas are, as when they're very soft, they move about quite readily, and that affects the relative accuracy of foot placement, in the case of a below-knee leg prosthesis. If the soft tissue is allowed to move about too freely, one can't rely on where the footfall will occur. A very small movement within the socket can have quite large impact on relative position of the heel.

One other limitation that has to be considered is that the process is not instantaneous. Dimensional changes in the stump due to swelling, which can be quite rapid, has to be taken into consideration, so getting it done quickly is quite essential.

When I said the spacing of the probes it to be on the order of 2 mm, I donsidered that an absolute minimum. I'm persuaded, first by manufacturing constraints, and secondly by limitations on incremental benefit of proximity beyond half-a-centimeter, that it should be in the region of 50 mm. For a proof of concept, I'd even consider 1 cm, which is on the somewhat more than 3/8-inch.

I would not consider moving the probe set while pressure is applied, due to the risk of tearing skin.

I'm not sure whether it's more important to measure the probes' deflection concurrently or one-at-a-time. I'm also not sure whether it's more beneficial to measure the probes on a horizontal plane or a vertical one. Both have potential benefit. I'm not even certain that it would be better to use one probe or many.

RE


List of 49 messages in thread
TopicAuthorDate
How would you do this?      Richard Erlacher      09/10/12 10:30      
   I have no idea if this would work, but ....      Erik Malund      09/10/12 10:32      
      How would one actuate them?      Richard Erlacher      09/10/12 12:29      
   strain guage      Mahmood Elnasser      09/10/12 11:03      
      Yes, you might be onto something.      Richard Erlacher      09/10/12 12:49      
         Computer-controlled?      Per Westermark      09/10/12 16:37      
            computer controlled      Richard Erlacher      09/10/12 19:52      
               Calibration + redundant force-limitation      Per Westermark      09/11/12 00:03      
               Interesting problem      Jim Granville      09/13/12 15:06      
                  Yes, it seemed coarse, at first.      Richard Erlacher      09/13/12 17:08      
                     Precision is cheap ?      Jim Granville      09/14/12 15:15      
                        I don't follow ...       Richard Erlacher      09/15/12 09:59      
                           Precision      Jim Granville      09/15/12 19:09      
                              other considerations      Richard Erlacher      09/15/12 20:15      
         Tomographic imaging?      Christoph Franck      09/11/12 04:47      
            There's one major problem ... maybe two ...      Richard Erlacher      09/11/12 09:20      
               $100 MRI unit      Erik Malund      09/11/12 09:31      
                  I'm not sure ...       Richard Erlacher      09/12/12 09:57      
         Voice coil and LVDT?      Oliver Sedlacek      09/12/12 02:37      
            Not having a lot of experience with this sort of stuff ...      Richard Erlacher      09/12/12 10:07      
               Danger/problems with hydraulic since no spring effect      Per Westermark      09/12/12 13:55      
                  A few things puzzle me with this approach      Richard Erlacher      09/13/12 02:07      
   Ultra Sound Probing      Michael Karas      09/10/12 16:36      
      Ultra-sound is better for measuring surface or sub-surface      Per Westermark      09/10/12 16:39      
   I would not use volumetric imaging      Justin Fontes      09/13/12 11:05      
      I'm not sure what you mean      Richard Erlacher      09/13/12 16:59      
         another thought      Rick Gebhardt      09/17/12 13:43      
            I consider that one of the more "pregnant" approaches      Richard Erlacher      09/17/12 15:25      
               Lots of options available      Per Westermark      09/17/12 16:14      
                  You've got to consider cost      Richard Erlacher      09/18/12 16:50      
                     Cost/safety      Per Westermark      09/18/12 18:29      
                     Cost target?      Oliver Sedlacek      09/21/12 08:37      
                        The price target comes from a few prosthetists      Richard Erlacher      09/21/12 21:46      
   comercial CMM      Mahmood Elnasser      09/17/12 13:58      
      This only received cursory examination       Richard Erlacher      09/17/12 15:28      
         pneumatic actuator      Rick Gebhardt      09/17/12 20:14      
            Yes ... but what would this cost?      Richard Erlacher      09/17/12 23:30      
               100 rods?      Per Westermark      09/18/12 02:04      
                  Patient size ...      Christoph Franck      09/18/12 06:12      
                     That's what I'm considering      Richard Erlacher      09/18/12 07:50      
                     AAACK! ... another double post ...       Richard Erlacher      09/18/12 07:50      
                  it's not as big as you think!      Richard Erlacher      09/18/12 07:40      
                     90% coverage      Maarten Brock      09/19/12 03:47      
                        So maybe vacuum pump for the too fat people      Per Westermark      09/19/12 06:38      
   I do not know if this is relevant, but      Erik Malund      09/19/12 07:52      
      I'll have to look into this.      Richard Erlacher      09/19/12 09:13      
         Single air pressure sensor sensor for tip force guestimate      Per Westermark      09/19/12 11:27      
   What about infrared?      Marshall Brown      09/21/12 03:03      
      How would you do this so it would retail for under $5k      Richard Erlacher      09/21/12 08:21      

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