(SEM VI) THEORY EXAMINATION 2021-22 THEORY OF MACHINE

SECTION A – Short Answer Notes (2 Marks Each)
 

1. Binary, Ternary and Quaternary Joint
 

A binary joint connects two links and permits relative motion between them, such as a pin joint.
A ternary joint connects three links at one point, reducing the number of joints required.
A quaternary joint connects four links at a single point and is rarely used due to complexity.

2. Interference

Interference occurs in gear teeth when the non-involute portion of one tooth comes in contact with the mating gear tooth. It leads to improper motion, noise, and wear and is avoided by limiting minimum teeth on the pinion.

3. Difference Between Flywheel and Governor

A flywheel controls fluctuations in speed within a cycle by storing and releasing energy.
A governor controls the mean speed of an engine by regulating fuel or steam supply.

4. Instantaneous Centre

The instantaneous centre is a point where two links have the same velocity at an instant. At this point, relative velocity is zero, and it is used to analyze planar motion.

5. Constrained Motion

Constrained motion is the motion of a link that is restricted to a definite path. Examples include piston movement in a cylinder and sliding pairs.

6. Types of Transmission System

Power transmission systems include belt drive, rope drive, chain drive, and gear drive. Each system differs in efficiency, slip, and load capacity.

7. Lower Pair and Higher Pair

A lower pair has surface contact (e.g., piston and cylinder).
A higher pair has point or line contact (e.g., cam and follower).

8. Degree of Freedom

Degree of freedom is the number of independent movements allowed to a mechanism. A plane mechanism generally has up to three degrees of freedom.

9. Coefficient of Fluctuation of Energy

It is the ratio of maximum fluctuation of energy to the mean energy stored in a flywheel. It indicates the energy regulating capacity of the flywheel.

10. Types of Follower

Followers are classified based on motion and contact, such as knife-edge, roller, flat-faced, and spherical followers.

SECTION B – Long Answer Notes (Attempt Any Three)

1. Quick Return Mechanism (Velocity & Expression)

A quick return mechanism allows the cutting stroke to take longer than the return stroke. This increases productivity in machines like shapers.
Velocity ratio depends on crank angles, and the return stroke occurs faster due to unequal angular movement.

2. Effort and Power of Governor

Effort of governor is the force required to change the position of the sleeve.
Power of governor is the work done at the sleeve for a given displacement.
A powerful governor responds quickly to load changes.

3. Absorption vs Transmission Dynamometer & Torsion Dynamometer

An absorption dynamometer absorbs power and converts it into heat (e.g., rope brake).
A transmission dynamometer measures power while transmitting it.
A torsion dynamometer measures torque based on shaft twist.

4. Porter Governor Numerical (Conceptual Explanation)

In a Porter governor, centrifugal force balances the combined weight of balls and sleeve.
Equilibrium speed depends on radius of rotation, ball mass, and sleeve mass.

5. Involute vs Cycloidal Teeth

Involute teeth maintain constant velocity ratio even with center distance variation.
Cycloidal teeth reduce wear but are harder to manufacture.

SECTION C – Long Descriptive Answers (Attempt One)

1. Balancing of Rotating Masses

Balancing involves placing a balancing mass such that the resultant centrifugal force becomes zero.
Vector diagrams and force polygons are used to determine balancing mass magnitude and position.

2. Mechanism and Inversion of Double Slider Crank Chain

A mechanism converts motion into useful work.
An inversion of a double slider crank chain includes elliptical trammel, which produces elliptical motion.

3. Gyroscope – Working and Application

A gyroscope works on the principle of angular momentum.
Applications include ship stabilization, aircraft navigation, and railway vehicle balancing.

4. Minimum Number of Teeth to Avoid Interference

Interference occurs when the line of action extends beyond the base circle.
The minimum number of teeth is derived using pressure angle and gear geometry.

5. Cam Profile for Roller Follower (UARM Motion)

The cam profile is drawn using uniform acceleration and retardation laws.
Maximum velocity and acceleration are calculated using cam speed and lift parameters.

6. Law of Gearing

The law states that the common normal at the point of contact must pass through the pitch point for constant velocity ratio.
Involute gears satisfy this law naturally.

7. Gear Trains and Epicyclic Gear Train

Simple, compound, reverted, and epicyclic gear trains differ in arrangement and speed ratio.
Epicyclic gear trains are compact and used in automobiles.