Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
Richard Erlacher
09/10/12 12:49
Read: 682 times
Denver, Co

#188297 - Yes, you might be onto something.
Responding to: Mahmood Elnasser's previous message
I suppose I could use a well-characterized spring driven by a cable on a stepper, which then would define the travel, and the strain gauge would define the pressure at that travel. Unfortunately, I need to measure at points about 50 mm apart, over a span of, perhaps, as much as 25 cm. Now it might be possible to get there with a few of these, but that would, I guess, require several passes along that 25 cm target. With a human body, the measurement doesn't need to be terribly precise where soft tissue is present, but where it is just bone under a thin skin, it's quite critical.

Does this appear to you to be something "doable" within the space constraint? Don't forget, it's a human body that's being measured, and we don't want to make holes or tears in the skin.

I'm thinking of a 25 cm steel bar with holes for the probes, and a fixture on which it can be rotated full circle, while holding the bar with the probes quite vertical, or, more specifically, in a precise relationship with the vertical while it is rotated about the member under study. The target is an amputation stump, which has to be fitted quite precisely about the hard regions, but which can be somewhat more "sloppy" in its fit about the soft tissue, when applying a prosthesis.

What's presently done is quite effective for relatively simply shaped stumps, but when there are bony protuberances, or other irregularities, it gets quite tricky, as, the way I've seen it done involves taking a negative cast, which preserves no information about the location of hard surface under a layer of skin and the location of relatively soft tissue. Subsequently, a positive cast is made, which then can introduce error, a socket is made from that, after considerable "modification" based on "educated guesses" about the character of the tissue in various places. This generally produces "adequate" results, but often breaks down.

I'm just curious as to whether it might be possible to "automate out" some of the guesswork.

I think this notion of yours is a good one and, combining deflection that's defined by, say, a stepper, with pressure feedback, from a strain gauge, might offer a good way to get a look at the problem. Unfortunately, the equipment then would be quite massive and prohibitive in its cost.

I know ... I know ... medically-related stuff always is ridiculously costly.

Thanks for the suggestion.


List of 49 messages in thread
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      

Back to Subject List