1UC BerkeleyKen Youssefi

Introduction to Mechanisms

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Mechanism

Machines are mechanical devices used to accomplish work. A mechanism is a heart of a machine. It is the mechanical portion of the machine that has the function of transferring motion and forces from a power source to an output.

Mechanism is a system of rigid elements (linkages) arranged and connected to transmit motion in a predetermined fashion.

Mechanism consists of linkages and joints.

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Example of Mechanism

Can crusher

Simple press

Rear-window wiper

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Example of Mechanisms

Moves packages from an assembly bench to a conveyor

Lift platformMicrowave carrier to assist people on wheelchair

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Example of Mechanisms

Lift platform

Front loader

Device to close the top flap of boxes

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Example of Mechanisms

Conceptual design for an exercise machine

Rowing type exercise machine

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Example of Mechanisms

Six-bar linkage prosthetic knee mechanism

Extension position

Flexed position

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Four-Bar Linkage

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Four-Bar Linkage Categories

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Four-Bar Linkage Categories

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4-Bar mechanisms

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4-Bar mechanismsS + l > p + q

4 double rocker mechanisms

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The Slider-Crank Mechanism

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Slider-Crank Mechanism

Offset slider-crank mechanism

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Slider-Crank Mechanism

In-line slider crank mechanism

The mechanism has a stroke B1B2 equal twice the crank length r2.

Locations B1 and B2 are called the extreme positions (limiting) of the slider

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The Slider-Crank Mechanism

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Slider-Crank Mechanism - Inversion

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Mechanism CategoriesFunction Generation Mechanisms

A function generator is a linkage in which the relative motion between links connected to the ground is of interest.

A four-bar hand actuated wheelchair brake mechanism

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Mechanism Categories

Function Generation Mechanisms

A four-bar drive linkage for a lawn sprinkler

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Mechanism CategoriesMotion Generation Mechanisms

In motion generation, the entire motion of the coupler link is of interest (rigid body guidance).

New Rollerblade brake system

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Mechanism CategoriesMotion Generation Mechanisms

Four-bar automobile hood linkage design

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Mechanism Categories

Path Generation Mechanisms

In path generation, we are concerned only with the path of a tracer point and not with the motion (rotation) of the coupler link.

Crane – straight line motion

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Primary Joints

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Higher Order Joints

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Motion Generation Mechanisms

Rotating a monitor into a storage position

Moving a storage bin from an accessible position to a stored position

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Motion Generation Mechanisms

Lifting a boat out of water

Moving a trash pan from the floor up over a trash bin and into a dump position

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Straight line Mechanisms

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Straight line Mechanisms

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Straight Line Mechanism

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Scotch Yoke Mechanism

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Geneva Mechanism

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Linear Geneva Mechanism

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Ratchet Mechanism

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Straight Beam Walking Mechanism

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Roller and Flat Follower Cams

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Cylindrical Cam Mechanism

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Gears – Rack and Pinion

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Gears

Worm Gear Sets Bevel gears Planetary Gear set

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V-8 Engine

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Type of Motion and Mechanisms

Translation to Translation

Most power sources that are readily available today are either of the pure rotational motion type, such as electric motor or hand crank, or of the pure translational type, such as pneumatic or hydraulic cylinder.

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Type of Motion and MechanismsRotational to Rotational

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Type of Motion and MechanismsRotation to Translation

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References• Mechanism Design, Analysis and Synthesis by

Erdman and sander, fourth edition, Prentice-Hall, 2001,

• Machines and Mechanisms by Uicker, Pennock and Shigley, third edition, Oxford, 2002.

• Machines and Mechanisms by Myszka, Prentice-Hall, 1999