(http://www.personal.reading.ac.uk/~shshawin/teaching/naturalrobotics) (http://www.personal.reading.ac.uk/~shshawin) (blackboard)

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)

Outputs (for your portfolio)

Weight compensation principles

The two methods to consider are

  1. Geometric springs [Rahman95]
  2. Non circular pulleys [Ulrich1991passive], [Endo2010passive]

Details are in the papers and will be reviewed online screencasts.


We will try arrange to send samples of the following to the nominated 'assembly' person.

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.


Michael Thomas, Thomas Müller and Martin W Busse, "Comparison of tension in Thera-band and Cando tubing", 2002 Journal of Orthopaedic & Sports Physical Therapy https://www.jospt.org/doi/pdf/10.2519/jospt.2002.32.11.576
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
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
T. Rahman, R. Ramanathan, R. Seliktar and W. Harwin, "A Simple Technique to Passively Gravity-Balance Articulated Mechanisms", 1995 Transactions of the ASME, Journal of Mechanisms Design http://pdfs.semanticscholar.org/355b/efef7024a5e5a61402222223fb9af855ae7b.pdf

W.S. Harwin 24/1/2021