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Best way to lift weight using mechanical arm

  1. Nov 26, 2013 #1

    For my finally year design project, I intend to try and solve the problems with existing shower bathing aids for the elderly and disabled. I won't go into details of what problems and how, etc, but I will give you an overview of the mechanism I intend to use.

    My product is essentially a chair attached to a motorised mechanical "arm" that has to lift the user over the side of the bath and inside. The arm could be attached to the wall alongside the bath, with support frames (e.g. http://www.geberit.co.uk/en_uk/targ...tallation_systems_1/installation_systems.html) concealed in the wall.

    The problem I want to solve is to figure out how to lift the user (up to 150 kg) in the most effective way possible. To try and solve it, I've looked at other products that support a heavy weight at the end of a bar. Things like

    Can anyone help me by suggesting a method/ mechanism to deal with this sort of weight/ moment at the end of a bar?

  2. jcsd
  3. Nov 26, 2013 #2


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    Staff: Mentor

    Welcome to the PF.

    This sounds like a wonderful and valuable project. Good for you. :smile:

    I'm wondering about why you have to be concerned at all about "lifting" though. A chair-height assist would not have to lift anybody over the ledge of a bathtub. A standing person could sit in a swivel chair, and swivel themselves across the bathtub ledge, and a wheelchair-bound person could transfer themselves from the wheelchair to the swivel chair, and into a chair in the bathtub...
  4. Nov 27, 2013 #3

    Hi! Thanks for your reply.

    The product that I'm designing needs to go beyond simple aids like the bath lift and the swivel chair. It's aimed more at someone who would have to consider installing a wet room to use a shower chair. Th project started off to improve upon the existing shower chairs, but research showed that shower chairs are really not necessary.
    Based on all my research and insights, I have decided to design a product that adapts to existing bathing environments, without being as industrial and un-dignified as some of the products available today.
    Do you have any idea how I would be able to design a mechanism to transfer someone into a bath while seated? If not, do you know how I would go about calculating the degree of support needed?

    I'm glad you appreciate the project. Hopefully I can verify a method that works and successfully build a working prototype!

    Last edited by a moderator: Nov 27, 2013
  5. Nov 27, 2013 #4


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    Gold Member

    You need to clarify your design objectives, operationally and economically.
    Berkeman has offered a reasonable and effective suggestion that addresses the problem you are focusing on.
    Now you are introducing difficult to quantify concepts, that it 'needs to adapt to existing bathroom environments, without being industrial and un-dignified'. These make the problem much more challenging.
    For most people, living in multi unit dwellings, the walls are non structural. That makes installing a people lifting mechanism an expensive proposition. A sliding chair over the side of the tub is a lot cheaper,
    even if it does not allow the user to actually sit in the tub, which a lifting mechanism might.
  6. Nov 27, 2013 #5
    Hi! Thanks for your reply.
    I do appreciate your help, but I am not looking for design advice anymore.
    I have thought of all these situations. The scope of my project, however, extends beyond a sliding chair. I have also taken costs in mind, but the product I am to design will be quite "up-market". I have also decided that the product will have to be fitted with supports inside the wall that will also supply power for the working mechanism (Google geberit).
    With all this considered, I need to now figure out what the best way to calculate and lift a heavy weight with a mechanical arm is. Can you help?

  7. Nov 27, 2013 #6


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    Science Advisor

    The usual way to control movement of heavy weights is with hydraulics. Cylinder lock valves prevent injury through catastrophic failures of the hydraulic system.
  8. Nov 27, 2013 #7
    Thank you very much! I was considering hydraulics. Will look into cylinder lock valves.
  9. Nov 27, 2013 #8


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    Staff: Mentor

    Can you share with us your cost/benifit analysis of the walk-in-tub retrofit versus what your are proposing in your project? You must have already considered that tradeoff or you would not be pursuing a lifting device to help the Pts into the tub...

    EDIT -- Adding link: http://www.safeguardtubs.com/?gclid=CKX9ud6-hrsCFUtp7AodV2EADQ

  10. Nov 27, 2013 #9


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    Science Advisor

    Cylinder lock valves, AKA “pilot operated check valves”. They fit directly to the cylinder to prevent fluid flow from the cylinder without hydraulic pressure from the control valve to the other side of the cylinder. They come as single or double. For your application where the cylinder is always loaded on one side you probably only need a single side protected. They are insurance against burst hoses and couplers.
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