MECHANISMS
motion produced by a motor is transformed and converted by mechanisms to receiving elements such as wheels
Linear motion mechanisms
Mechanisms are devices that transmit and convert forces and motion from driving force or input element to an output element
diverse uses
most important element in all of them is the driving force, for example a string
entertaining children in the park
lifting and carrying objects
Transporting people from A to B
telling the time
Fixed pulley
Movable pulley
levers
F is the force or effort applied at one end of the bar
R i s the resistance or load which acts at the other end of the bar
rigid bar that is supported by a fulcrum.
d is the distance from F to the fulcrum
r is the distance from R to the fulcrum
equation: F d= f · r
type of levers:
Class 2: resistance is between the fulcrum and effort applied.Effect of the effort applied is always multiplied
Class 3:effort applied is between the fulcrum. Effect of the effort applied is always reduced.
Class 1: fucrum is between the effort applied and the resistance.Effect of the effort applied can be multiplied or reduced
F=R
Used to raise and lower loads easily
is a wheel that has a groove around lt into which a rope,
cham or belt fits It rotates around an axle that is fixed to an immobile surface
example: wells and gym equipment
equation: F=R/2
effort required to move a load is half the effort needed to move the same load with a fixed pulley.
is a set of two pulleys — one is fixed while the other
can move in a linear direction.
Compound pulley
more pulleys, system becomes more complex, but less
effort is needed to move the load
(n = the number of movable pulleys).
is a system of fixed and moveable pulleys, often called block and
tackle.
example: lifts
Rotary motion mechanisms
Worm gear
Gear mechanisms and cogwheels
Friction drives
Pulleys with belt
transmit motion and effort in a circular way
Gear mechanisms with a chain
first wheel is called the primary drive wheel. When it moves, it
turns or drives the second or output wheel, causing it to move as well.
N, D, = N, Dr-->D1/D2=N1/N2
are made up of two or more wheels that are in contact
N1 and N2 are the velocities of the primary drive wheel
D1 ans D2 are the corresponding diameters
axles are parallel and they rotate simultaneously due to the effect
of the belt.
rotation of one axle is transmitted to the other through the
connected pulleys.
consist of two pulleys or wheels that are a certain distance apart.
Uses: industnal machines
cogs fit into the spaces between the cogs of another wheel,
They transmit a rotary motion between the two connected axles
Cogwheels are sets of wheels that have teeth called cogs.
Gears can be cylindncal or conical.
N, Z ,=N ,.Z-->Z,/Z2=N2/N1
N, and N, are the velocities of the corresponding wheels.
Z1 and Z2 are the numbers of teeth.
Nwheel=Nscrew.Zgrooves/ Zwheel
is a screw that moves a helical cogwheel that is set perpendicular to the screw
N„„ , and N „„ are the velocities of the wheel and of the screw
Z, „ is the number of grooves of the screw and Z„„, is the number of teeth of the wheel
are two cogwheels with parallel axles that are a certain distance apart
N, Z, = N, Z--> Z1/Z2=N2/N1
N an d N, are the velocities of the corresponding wheels
Z a nd Z, are the number of teeth
Gear train
N4/N1=Z1xZ3/Z2xZ4
N, and N, are the velocities of the dnve wheel and the driven wheel.
This is a system of more than two gears, connected together as shown in the diagram
Z , Z,, Z, and Z„are the number of teeth on the wheels.
Pulley trains with belts
N1 and N, are the respective velocities of the drive and driven
pulleys.
De Dn Di and D, are the diameters of each wheel
N4/N1=D1xD3/D2xD4
Rotary motion is transmitted to axle to by the belt
Pulleys 2 and 3 same velocity
belt transmt motion of pulley 3 to 4
whells rotate at same direction
Variation in velocity
Constant system
Reducing system
Multiplying system
MECHANISMS THAT TRANSFORM MOTION
From rotary into reciprocating motion
click to edit
From rotary into lineal
Nut and bolt system
winch and crack handle
rack and pinion system
L= PxZxN
L is the velocity of the rack's movement in millimetres per
minute
uses a pinion that is a small cogwheel, mounted on a rack
P is the distance between two consecutive teeth in millimetres.
Z is the number of teeth in the pinion.
N is the number of rotations per minute of the pinion
bolt or threaded bar and a nut that has the same
intenor diameter as the diameter of the bolt.
consists of a drum that rotates and acrank handle that allows to pull or lift obiects
F d= R . r -->F=R. Rxr/d
A crack is a bar attached to an axle that is used to turn it
F is the force applied and R, the resistance.
r is the radius of the winch and d, the length of the crank handle.
Crankshaf
Crank-link-slider
rod has articulated Ioints at each end
As the wheel rotates, the crank transmits the rotary motton to the
connecting rod
is composed of a crank and a rod called a connecting rod or link.
is a set of connecting rods attached to a jointed axle. Each of the
points of the axle acts as a crank.
A crankshaft transforms the rotary motion of an axle into a
reciprocating motion with different connecting rods
Cam
We can change the shape and the usable profiles
A cern transforms rotary motion
into reciprocating motion in the follower or bar
is a rotating object that pushes a follower as it moves
A set of cams fixed on the same axle is called a camshaft
Eccentric cam
transforms the rotary motion of the
wheel into reciprocating motion in the follower
This consists of a wheel with an off centre rotation axle
OTHER MECHANISMS
Mechanisms that store energy
Connecting mechanisms
Mechanisms for controlling and directing motion
Disc brakes consist of pads and a disc anached to the oblect that we want to slow down
Brand brakes consist of a metal band that puts pressure on drum attached to the axle of the oblect
most typical mechanism is ratchet
Drum brakes include one or two brake shoes that come into
contact with the drum.
By compression
By traction
Springs are devices that absorb energy
By torsion
Fixed connections are used to make permanent connections
between axles and shafts
Mo v able connections are used to connect shafts that can move
along the axle or at an angle to each other
Clutches are mechanisms that allow axles or shafts to be connected or separated
Supports: bushings and bearings
Bearings are made up of two concentric nngs with balls or rollers
between them
In bushings the axle or the shaft is inserted in a plain circular piece that is placed inside a housing to provide a bearing surface.
