Design challenge 2: A gravity compensation mechanism
Mechanical compensation of weight can be invaluable in rehabilitation and assistive technologies. The Wilminton Rehabilitation Arm Orthosis is one example where this idea has been combined with rapid design and 3D printing. However there are other mechanisms that also enable gravity compensation that may be more customisable to a particular need, in particular providing a way to adapt the mechanism so it has an adjustable preferred height.
What is WREX (Narrated by Tariq Rahman)WREX: Emma's magic arms
The second challenge is to investigate, design and build in simulation, a prototype mechanism to demonstrate weight compensation that could be used as an assistive exoskeleton. Two mechanisms for weight compensation will be discussed in class, and should be considered by the team. The design team should consider these principles and any others that might work and base their designs on that principle. There will be weekly design review meetings, with a detailed reviewed in week 4/5 when it may be possible to then 3D print and assemble a working prototype.
Teams of two to three people (exceptionally more)
The team should create and define what an eventual 'product' should achieved using a product definition statement (PDS).
The PDS should consider how to achieve a weightless arm, that can be overlaid with a low level stiffness. The centre point of this stiffness should be adjustable to be in the persons working zone, e.g. just over a table.
The team should identify some 'user experience' outlines to consider the product from the users perspective.
Each person in the team should build at least one 'paper and string' rapid prototype to ensure any ideas will work.
Teams should analyse both proposed methods (non circular pulleys or geometric springs) and choose one to build
Designs should utilise bearing kits and include either plain or ball bearing joints.
All parts of a working prototype should be designed in fusion 360 and an assembly created.
Each team member should show that a stress analysis can be done on one of the parts of the final design.
Outputs (for your portfolio)
Videos, pictures, 3D renderings, stl files, etc.
A short outline of your contributions, calculations and thoughts (cannot be shared)
NOTE: The PDS and the user experience stories can be shared between portfolios, but all team members must be credited on this/these documents.
Details are in the papers and will be reviewed online screencasts.
Materials
We will try arrange to send samples of the following to the nominated 'assembly' person.
A sample of 250mm rods of varying materials. These should form the main structure of your design.
An M6 ball bearing kit
An M4 ball bearing kit
An M4 plain bearing kit
It may be possible to arrange a selection of Theraband tubing as a possible spring material (yellow, blue, red) [Thomas2002comparison]. Alternatively design for standard office elastic bands.
Otherwise, where possible, please keep parts to things that you can find around the house or get locally (e.g. elastic bands, wood). Even though this is intended to be a digital design, we would like to keep open the possibility of assembling the prototype.
Gen Endo, Hiroya Yamada, Akira Yajima, Masaru Ogata and Shigeo Hirose, "A passive weight compensation mechanism with a non-circular pulley and a spring", 2010 2010 IEEE International Conference on Robotics and Automation https://ieeexplore.ieee.org/document/5509797
[Ulrich1991passive]
N. Ulrich and V. Kumar, "Passive mechanical gravity compensation for robot manipulators", 1991 Robotics and Automation, 1991. Proceedings., 1991 IEEE International Conference on 10.1109/ROBOT.1991.131834