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Research into compliant bistable mechanisms with the application in the design of an easy-chair

Lassche, T.J. (2015) Research into compliant bistable mechanisms with the application in the design of an easy-chair.

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Abstract:In the world many elderly suffer from arthritis. For these people, the stresses that develop in their limbs when rising from a chair can be uncomfortably high. While there are several existing chairs designed to address this problem, most use electrical actuators or complex hydraulic systems. Since electrical power is not available everywhere for the entire day, especially in developing countries, there is a need for an easy-chair that gives support during rising from the chair without using electrical power. I worked for about three months at the Indian Institute of Science on a project of prof. G.K. Ananthasuresh to design an easy-chair for the elderly, without the need of electrical power. I did research into compliant mechanisms and its bistable behavior, to use this for the design of a seat for an easy-chair. A compliant bistable mechanism can have two stable positions, where one state is stress-free while the other state stores potential energy. Using the stress-free state of the seat as the upper position and the other state as the seated (lower) position, the energy stored in the mechanism can be used to support the occupant while rising from the chair - going from the seated position up to the upper position. The energy can be released using an addition force of the occupant on the armrests of the chair. To achieve this, a two-port bistable compliant mechanism is developed, where the forces to switch between the two states differs for the two ports of actuation (the seat and the armrests). Additionally, the seat is statically balanced, to reduce the required stiffness of the compliant part and increase the flexibility of the chair for different weights of the occupant. Both a one and two degree of freedom model is developed to describe the behavior of the two-port bistable compliant mechanism. The one degree of freedom model and its application in the easy-chair is described in a paper submitted to the IFToMM congress 2015. A scaled prototype of the easy-chair is developed to test the concept. The use of a two-port bistable compliant mechanism is interesting to gain mechanical advantage with compliant mechanism while switching between the two stable states. Using proper design of the different ports of actuation and the storage of energy in one of the stable states, the implementation of two-port bistable compliant mechanisms can be useful for many purposes.
Item Type:Internship Report (Master)
Indian Institute of Science, India
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Keywords:Modelling of compliantt bistability, static balancing, geriatric sit-to-stand chair
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