Compliant Mechanism and its applications is also an emerging topic in Engineering and space applications. This presentation gives an in-depth information on Compliant Mechanisms covering its properties, characteristics and various other aspects including their advantages, disadvantages, manufacturing techniques etc.

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Abhishek W.

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What is Compliant
Mechanism?

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• In Engineering, Compliant Mechanisms are
flexible mechanisms that transfer an input force
and displacement at one port to an output force
and displacement at another port through elastic
body deformation.
 So basically, Compliant Mechanisms don’t depend on
different parts as in Rigid Mechanisms, comprising of
parts which need an intermediate to transfer force.
 It has great number of applications in space missions,
medical field, engineering, robotics, nuclear weapons
etc.

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ADVANTAGES OF COMPLIANT
MECHANISM

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1) Reduced Part Count
 Compliant Mechanisms have the potential to
dramatically reduce the total number of parts required
to accomplish a particular task.
 It is generally done by having flexible parts instead of
springs, pins, and traditional rigid hinges.
 Therefore, the no. of components required for
Compliant Mechanism < Rigid Mechanism

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Compliant Mechanism Gripper
Input Force/Output Force = 1/30 (approx)

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2) Easy to Manufacture
 Compliant Mechanisms are easy to manufacture
because they can be produced using various
manufacturing processes.
 Many Compliant Mechanisms can be fabricated flat
from planar sheets of material.
 Manufacturing methods including machining,
stamping, laser cutting, water-jet cutting, 3D printing
and EDM can be used to manufacture these
mechanisms.

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3) Lower Price
 Because of the reduced part count and simple
manufacturing processes involved in compliant
mechanisms they are inexpensive.
 The optimisation of fewer parts and simple
manufacturing techniques reduce the assembly time
and cost.

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4) Precise Motion
 Compliant Mechanisms allow precise motion by
reducing or eliminating backlash and wear.
(Backlash is caused by the tolerances of
interconnecting pieces)
 Mechanical wear that happens in rigid body
mechanism is not seen in compliant mechanism as
there are no interconnecting parts such as hinges as in
rigid body and thus minimises the wear even further.

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5) Performance and Maintenance
 Compliant Mechanisms have smaller no. Of movable
joints(such as pin) which results in reduced friction.
 This also reduces the need for lubrication.
 This valuable characteristic can help in applications
where the mechanism is not easily accessible as in
harsh environments.
 As in space where lubricants tend to “outgas” in a low-
gravity environment.

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- Thrusters using compliant mechanism for rotation

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6) Micro Applications
 Another advantage of Compliant Mechanism is that
they can be easily miniaturized.
 Simple micro structures, actuators, and sensors are
seeing wide use and also the micro electromechanical
system shows great promise with the help of compliant
mechanism.
 Here too, the reduced parts is a significant advantage
of the compliant mechanism.

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7) Portability
 A significant reduction in weight can be observed by
using compliant mechanism over their rigid-body
counterparts.
 This has a lot of scope in the aerospace industry as a
major concern in payloads and weight is seen in
rockets and aircrafts.
 It has also benefitted companies by reducing the
weight and shipping costs of customer products.

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Compliant Mechanism Gripper A Rigid-Body Mechanism Plier

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CHALLENGES OF COMPLIANT
MECHANISMS

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1) Designing Complex System
 There is a relative difficulty in analyzing and designing
of compliant mechanisms.
 Knowledge of mechanism analysis methods and
deflection of flexible members is required.
 You need to understand the interactions in a complex
system before combining any two bodies comprising
of compliant mechanism.

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2) Analysis of Compliant
Mechanism
 Linearized beam equations are not valid in case of
Compliant mechanisms as many of the flexible
members undergo large deflections.
 Many Compliant Mechanisms in the past were
designed by trial and error approaches.
 Theories have been developed to simplify this but still
considering these advances, analysis and design of
compliant mechanism is lot harder than rigid-body
mechanism.

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3) Energy Storage and Fatigue
 Compliant Mechanisms are used to store energy but in
some cases though some energy gets stored in the
mechanism and does not reach till the output end thus
decreasing its efficiency.
 As compliant members are often loaded cyclically it is
important to design those members that they will have
sufficient fatigue life to perform their functions.

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4) Limited Motion
 Motion from deflection of the compliant links are
limited by the strength of deflecting members.
 Compliant link cannot produce a rotational motion
such as that possible with a pin point.

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DESIGNING COMPLIANT
MECHANISMS

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Compliant Mechanisms are usually designed using
2 techniques:
- Pseudo-rigid body model
- Topology Optimization

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Pseudo-Rigid Body Model
 This method was introduced by Larry. L. Howell in
1994.
 It is an approximation technique for modelling a
compliant mechanism rather for those where
compliant joints experience large deflection and leads
to non-linear behaviour.
 It enables the simulation of complicated non linear
elastic behaviours using well established and
comparatively simple methods.

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Topology Optimization
 Topology optimization refers to software that takes
advantage of the design freedoms offered by additive
manufacturing.
 In general, topology optimization programs enable
designers to create a design that is strong.
 One of the key benefits of topology optimization is its
ability to cut excess weight out of the design.
 General Electric once removed 84% of weight from an
engine bracket using topology optimization.

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Bistable Compliant Mechanisms
 These Mechanisms have two stable equilibrium
positions within their range of motions.
 Its main advantage is-
Ability to stay in two positions without power input
and despite small external disturbances.
 Designing these mechanisms require solving non-
linear differential eqn and consideration of energy
storage and motion requirements.
 It has proved of a great advantage in many micro-
electromechanical systems(MEMS).

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A Switch made out of Compliant
Mechanism

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Compliant Mechanism ‘Clutch’

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3D Printed Titanium Structure

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To Know More On Compliant
Mechanism
Visit
Compliant Mechanism Analysis | Zap-Science

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