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Independent  Study

Compliant mechanism structure design and force transmission

By Tom

Abstract

Throughout the design process, we aim to strike a balance between structural stability and range of motion for users’ legs. This ensures the device is comfortable for elderly users while fully guaranteeing their safety. To fulfil both sides requirements, I start to get in touch and dig deep into compliant mechanism.

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Screenshot 2026-05-27 at 9.06.28 PM.png

Introduction of compliant mechanism

compliant mechanism transmits motion/force through elastic deformation of flexible elements (no traditional rigid joints), delivering advantages like high precision, zero friction, compactness, and ease of miniaturization.

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Design Principal and requirement

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Motion direction

A pushing motion from elderly will be done, so a compression motion is needed inside the mechanism

Travel distance

~5-10cm is needed

Structure Force needed

~20N will need to be provided (data from our year project)

Other functions

After extension, the outer part of the structure have to become somehow rigid to provide support.

My Design

  1. The feet will step on the structure at the top plate (in the reality will put it in horizontal)

  2. After stepping on, an around 20N force will be provided and start to push and slide the triangle part down.

  3. During the second process, parts highlighted in blue colour will start to extend and stretch as the structure is deformed.

  4. When reaching the end of the guide, a complete reaction forces feedback to the user.

  5. Also to prevent user over stepping on the structure, the side bar of the triangle structure can be bent to provide buffer distance.

Material
chose

PLA + TPU 90A

  • As PLA can provide the solid part of the structure and TPU 90A can provide the flexibility and rebound force for it.

  • the Blue part highlighted will be using TPU 90A and other part mainly will be PLA

  • In the connection of PLA and TPU the ratio of TPU will decrease in gradient with cross printing method

  • The side bar of the triangle will use mix materials, ratio around 3:7

Data

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Pros and Cons

Pros:

  • One Piece structure

  • less friction between different components

  • Flexible design freedom

  • lower cost

Cons:

  • Longer iteration time

  • Material creep issue, slow deform in long term

  • Poor repairability

ISDN2001/2002: Second Year Design Project

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