Ken YoussefiUC Berkeley 1 Introduction to Mechanisms.

1UC BerkeleyKen Youssefi

Introduction to Mechanisms

Ken Youssefi UC Berkeley 2

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.

Example of Mechanism

Can crusher

Simple press

Rear-window wiper

Example of Mechanisms

Moves packages from an assembly bench to a conveyor

Lift platformMicrowave carrier to assist people on wheelchair

Lift platform

Front loader

Device to close the top flap of boxes

Conceptual design for an exercise machine

Rowing type exercise machine

Six-bar linkage prosthetic knee mechanism

Extension position

Flexed position

Four-Bar Linkage

Four-Bar Linkage Categories

4-Bar mechanisms

4-Bar mechanismsS + l > p + q

4 double rocker mechanisms

The Slider-Crank Mechanism

Slider-Crank Mechanism

Offset slider-crank mechanism

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

The Slider-Crank Mechanism

Slider-Crank Mechanism - Inversion

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

Mechanism Categories

Function Generation Mechanisms

A four-bar drive linkage for a lawn sprinkler

Mechanism CategoriesMotion Generation Mechanisms

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

New Rollerblade brake system

Mechanism CategoriesMotion Generation Mechanisms

Four-bar automobile hood linkage design

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

Primary Joints

Higher Order Joints

Motion Generation Mechanisms

Rotating a monitor into a storage position

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

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

Straight line Mechanisms

Straight Line Mechanism

Scotch Yoke Mechanism

Geneva Mechanism

Linear Geneva Mechanism

Ratchet Mechanism

Straight Beam Walking Mechanism

Roller and Flat Follower Cams

Cylindrical Cam Mechanism

Gears – Rack and Pinion

Worm Gear Sets Bevel gears Planetary Gear set

V-8 Engine

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.

Type of Motion and MechanismsRotational to Rotational

Type of Motion and MechanismsRotation to Translation

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

Ken YoussefiUC Berkeley 1 Introduction to Mechanisms.

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