1. MECHANISM
GUNJAN VED
VENUGOPAL

2. A mechanism is a device designed to transform input forces and movement into a desired set of output forces and movement .
Mechanisms generally consist of moving components such as gears and gear trains, belt and chain drives, cam and follower mechanisms, and linkages .
Primary function of a mechanism is to transmit or to modify motion

3. TYPES OF MECHANISM Gear and gear train mechanism
Cam and follower machanism
linkages

4. Types of gear and gear train
Spur gear: gear with radial teeth parallel to its axis

5. Rack & Pinion a toothed wheel (pinion) engages a notched bar (rack) to convert rotary motion into linear motion.
Worm gear :A worm is used to reduce speed. For each complete turn of the worm shaft the gear shaft advances only one tooth of gear.

6. Helical gear: a gear that has the teeth cut at an angle to the center line of the gear

7. Nomenclature of gear
Pitch circle: A circle the radius of which is equal to the distance from the gear axis to the pitch point.
„ Addendum circle: A circle bounding the ends of the teeth, in a right section of the gear.
„ Root (or dedendum) circle: The circle bounding the spaces between the teeth, in a right section of the gear.
„ Addendum: The radial distance between the pitch circle and the addendum circle.
„ Dedendum: The radial distance between the pitch circle and the root circle.
„ Clearance: The difference between the dedendum of one gear and the addendum of the mating gear

8. Gear trains
Combination of two or more gears when they made to mesh each other to transmit power from one shaft to another.
TYPES OF GEAR TRAIN
Simple gear train
Compound gear train
Reverted gear train
Epicylic gear train

9. Simple gear train :
When there is only one gear on each shaft.
The only function of the idler gear is to change the direction of rotation. It has no affect on the gear ratio.

10. Compound gear train :
When there are more than one gear on a shaft,it is called a compound gear train.

11. Reverted gear train :
When the axes of the first driver and the last driven are co-axial, then the gear train is known as reverted gear train.
In a reverted gear train, the motion of the first gear and the last gear is same

12. Epicyclic gear train :
Epicyclic means one gear revolving upon and around another. The design involves planet and sun gears as one orbits the other like a planet around the sun.
A small gear at the center called the sun, several medium sized gears called the planets and a large external gear called the ring gear.

13. Advantages
Simple gear train :
To obtain desired direction of motion of the driven gear ( CW or CCW)
and to obtain high speed ratio.
Compound gear train :
A much larger speed reduction from the first shaft to the last shaft can be obtained with small gear.
If a simple gear trains used to give a large speed reduction, the last gear has to be very large.
Reverted gear train :
The reverted gear trains are used in automotive transmissions, lathe back gears, industrial speed reducers, and in clocks (where the minute and hour hand shafts are co-axial).

14. The simplest and basic is four bar chain mechanism
linkages
The function of a link mechanism is to produce rotating, oscillating, or reciprocating motion from the rotation of a crank or vice versa
The simplest and basic is four bar chain mechanism

15. Some important concepts in link mechanisms are:
Crank: A side link which revolves relative to the frame is called a crank
Rocker: Any link which does not revolve is called a rocker.
Crank-rocker mechanism: In a four bar linkage, if the shorter side link revolves and the other one rocks (i.e., oscillates), it is called a crank-rocker mechanism.
Double-crank mechanism: In a four bar linkage, if both of the side links revolve, it is called a double-crank mechanism.
Double-rocker mechanism: In a four bar linkage, if both of the side links rock, it is called a double-rocker mechanism.

16. s = length of shortest bar
l = length of longest bar
p, q = lengths of intermediate bar
Grashof's theorem states that a four-bar mechanism has at least one revolving link if s + l <= p + q and all three mobile links will rock if s + l > p + q

18. CAM AND FOLLOWER
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel (e.g. an eccentric wheel) or shaft that strikes a lever at one or more points on its circular path

19. The cam can be seen as a device that translates from circular to reciprocating motion.
 A common example is the camshaft of an automobile, which takes the rotary motion of the engine and translates it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders.

21. Types of cam and follower
                                                         
Figure 6-2 Classification of cam mechanisms
Types of cam and follower
Knife edge follower
Roller follower
Flat faced follower
Spherical faced follower
Offset follower
Rotating follower

22. CAM NOMENCLATURE

23. Trace point: It is used to generate the pitch curve.
Pitch curve: The path generated by the trace point at the follower is rotated about a stationary cam.
Pitch circle: A circle from the cam center through the pitch point. The pitch circle radius is used to calculate a cam of minimum size for a given pressure angle.
Prime circle (reference circle): The smallest circle from the cam center through the pitch curve.

24. Base circle: The smallest circle from the cam center through the cam profile curve.
Stroke :The greatest distance or angle through which the follower moves or rotates.
Pressure angle: The angle at any point between the normal to the pitch curve and the instantaneous direction of the follower motion.

25. BASED ON THE MOTION OF FOLLOWERS
SIMPLE HARMONIC MOTION
CONSTANT ACEELERATION & DECCELERTION
CONSTANT VELOCITY
CYCLOIDAL MOTION

27. APPLICANTIONS OF CAMS
AUTOMATIC MACHINES
INTERNAL COMBUSTION ENGINES
PRINTING CONTROL MECHANICS
MACHINE TOOLS