Machine and Mechanisms

Introduction to mechanisms and Kinematics

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KinematicsKinematics

It is the study of motion (relative motion of different links), quite apart from forces which produce that motion. More particularly, kinematics is the study of position, displacement, rotation, speed, velocity and acceleration which arise in the design of mechanical system, or kinematics of machine.

Kinematic analysis Determine

Position, displacement, rotation, speed, velocity, acceleration Provide

Geometry dimensions of the mechanism Operation range

Dynamic analysis Power capacity, stability, member load

Planar mechanism – motion in 2D space

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Machines and mechanismsMachine

Oxford dictionary: an apparatus for applying mechanical power, consisting of a number of interrelated parts each having a definite function.

Devices used to alter, transmit, and direct forces to accomplish a specific objective

Mechanical advantage is sole object of a machine e.g. lathe, shaper, planer etc.

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Is Engine also a machine

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?

Machines and mechanismsMechanism

Mechanical portion of a machine that has the function of transferring motion and forces from a power source to an output

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Wind shield

Simple Mechanism

Let's make a simple mechanism with similar behavior. Take some cardboard and make four strips as shown in. Take 4 pins and assemble them as shown in fig Now, hold the 6in. strip so it can't move and turn the 3in. strip. You will see that the 4in. strip oscillates.

Loader 4 bar mechanism

Slider crank mechanis

crank & piston

Block feeder

Mechanism terminologyLinkageFrameLinks– rigid bodyJointPrimary joint (full

joint)Revolute joint (pin or

hinge joint)– pure rotation

Sliding joint (piston or prism joint)– linear sliding

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Mechanism terminology cont

Higher-order joint (half joint)Allow rotation and

slidingCam jointGear connection

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Mechanism terminology cont

Simple linkA rigid body contains

only two jointsCrankRocker

Complex linkA rigid body contains

more than two jointsRocker armBellcrank

Point of interestActuator

A power source link

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Kinematic diagrams

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