Lever and Linkage Systems Principles of EngineeringTM Unit 4 – Lesson 4.1 - Mechanisms Forging new generations of engineers Project Lead The Way, Inc. Copyright 2007

Lever and Linkage Systems Methods of Power Transmission

The 3 Classes of Levers Each class has the fulcrum, effort and load arranged in a different way. The three classes are:

Class 1 Lever Fulcrum between the load and the effort

Class 2 Lever Load between the fulcrum and the effort

Class 3 Lever Effort is between load and fulcrum

ROCKER ARM Has an input and output arm which rock around a fulcrum point Acts as a link which transmit force or motion between moving parts Operate usually as a first class lever Change linear input motion to an opposed linear motion

BELL CRANK A bent first class lever that pivots at the bent point or elbow Used to change the direction of force or motion 90 degrees or less Used to convert rotary motion to straight line or reciprocating motion

BELL CRANK Reciprocating motion Top pin A moves slider to right pin B moves bell crank which moves slider to left Bottom pins move crank; spring returns to start position

DOUBLE BELL CRANK PUSH, PULL TYPE PUSH requires stiff connecting rods can use flexible wires,cables, ropes

DIFFERENTIAL LINKAGE Used to combine several motion inputs into a resulting output Three pivot points, none of which are fixed but are free to float within limits Any pivot can function as an input A motion control mechanism rather than a means of transmitting force or power

Types of four-bar linkages: PARALLEL LINKAGE SCISSOR LINKAGE (Whatever the motion, each point on a moving link must move in the same PLANE, and all the links must be parallel) Types of four-bar linkages: PARALLEL LINKAGE SCISSOR LINKAGE

FOUR-BAR LINKAGES To make a four-bar linkage a usable device, one of the four links, or one of the pivots, must be fixed Depending on the fixed pivot or link different motion outputs will occur

FOUR-BAR LINKAGES Fixed link links pivoting from the ends of the fixed link are either input links or input and output links the moving link opposite the fixed link is the connecting link

FOUR-BAR LINKAGES FIXED PIVOT the point opposite the the fixed point is normally the output point the remaining two pivot points are usually the input points

PARALLEL LINKAGE To provide parallel motion of a line or a surface as the linkage moves about two controlled pivot points The arms remain parallel through the operation of the connecting link Eg: man lift, robot gripper

SCISSOR LINKAGE To change the direction of a linear motion input to a linear motion output that is perpendicular to the input Large motion output (distance advantage) with a small motion input Especially true of a series of connecting linkages One fixed pivot point

SCISSOR LINKAGE Two pair of links of different length Less force at input pivot point - close to pivot point output is identical

SCISSOR LINKAGE Two pair of links of different length More force at input pivot point - farther from pivot point output is identical

WATT STRAIGHT LINE MOTION Does not form a parallelogram but consists of two equal length pivoting links and a connecting link Produces a straight line motion in the connecting link

Latching Non-latching TOGGLE LINKAGE Latching Non-latching

TOGGLE LINKAGE LATCHING capable of snap action from one state to an alternate state arm length may be different may have a toggle stop to produce latched condition

TOGGLE LINKAGE NON-LATCHING operated so that the two toggle arms never quite straighten may have a toggle stop to produce latched condition e.g. rock crushers hay balers