Cams MCQ Quiz in தமிழ் - Objective Question with Answer for Cams - இலவச PDF ஐப் பதிவிறக்கவும்

Explanation:

Cam and Follower 

• A rotating machine element which gives reciprocating or oscillating motion to a second element is known as cam.
• The second element is called a follower.
• The cam usually rotates at a constant speed and drives the follower whose motion depends upon the shape of the cam.
• Almost always the cam is driver and follower is driven.

According to the shape the cam can be classified as.

• Wedge and flat cams -  In this type of cam follower arrangement, a wedge cam has a translational motion and the follower can either translate or oscillate.

• Radial or Disc cams - A cam in which the follower moves radially from the centre of rotation of the cam is known as a radial or disc cam.

• Cylindrical cams - In a cylindrical cam, a cylinder which has a circumferential contour cut in surface, rotates about its axis. It is also known as barrel or drum cams.

• Conjugate cams - It is a double-disc cam and preferred when the requirements are low wear, low noise, better control of the follower, high speed, high dynamic loads, etc.
• Globoidal cams - It has two types of surface, convex or concave. It is used when the moderate speed and angle of the oscillation of the follower are large.

Concept:

• The Pressure angle is defined as the angle between the normal to the pitch curve at a point and the direction of the follower motion.
• Its values depends on the angle of ascent, the lift of the follower and offset between centre lines of cam and follower.
• Pressure angle varies in magnitude at all instants of the follower motion.

Concept:

Stroke or throw: The greatest distance or angle through which the follower moves or rotates. It is the maximum distance of followers from the base circle.

Explanation:

The following term is used with reference to the angular motion of the cam. 

Angle of Ascent:

It is the angle through which the cam turns during the time follower rises.

B - D represents ascent.

Angle of Dwell: 

It is the angle through which the cam turns while the follower remains stationary at the highest or the lowest position.

D - E represents dwell.

Angle of Descent:

It is the angle through which the cam turns during the time the follower returns to the initial position.

E - G represents Descent.

Explanation:

A cycloidal is the locus of a point on a circle rolling on a straight line.

Mathematically,

Acceleration in the cycloidal profile is expressed by:

a = \(\frac{{2\pi h{\omega ^2}}}{{{\varphi ^2}}}\;\sin \left( {\frac{{2\pi \theta }}{\varphi }} \right)\)

where:

h = Maximum follower displacement

ω = Angular velocity of cam

ϕ = Angle for the maximum follower displacement for cam rotation

This acceleration at \(\theta = \frac{\phi }{4}\)

Maximum acceleration is

a_max \(= \frac{{2\pi h{\omega ^2}}}{{{\varphi ^2}}}\;\sin \left( {\frac{{2\pi }}{\varphi } \times \frac{\phi }{4}} \right)\)

a_max = \(\frac{{2\pi h{\omega ^2}}}{{{\varphi ^2}}}\)

Pitch Circle: It is the circle passing through the pitch point and concentric with the base circle.

Pitch Curve: It is the curve drawn by the trace point assuming that the cam is fixed, and the trace point of the follower rotates around the cam i.e. if we hold the cam fixed and rotate the follower in a direction opposite to that of the cam, then the curve generated by the locus of the trace point is called pitch curve.

For a knife-edge follower, the pitch curve and the cam profile are same whereas for a roller follower they are separated by the radius of the roller.

Prime Circle: The prime circle is the smallest circle that can be drawn so as to be tangential to the pitch curve, with its centre at the cam centre.

Base Circle: It is the smallest circle, keeping the centre at the cam centre, drawn tangential to cam profile. The base circle decides the overall size of the cam and thus is fundamental feature.

Concept:

Uniform velocity motion

Simple harmonic motion

Cycloidal motion

Explanation:

The following term is used with reference to the angular motion of the cam. 

Angle of Ascent:

• The angle moved by the cam from the instant the follower begins to rise, till it reaches its highest position.
• B - D represents ascent.

Angle of Dwell:

• It is the angle through which the cam turns while the follower remains stationary at the highest or the lowest position.
• D - E represents dwell.

Angle of Descent:

• It is the angle through which the cam turns during the time the follower returns to the initial position.
• E - G represents dwell.

Explanation:

Cam and Follower 

• The rotating machine element which gives reciprocating or oscillating motion to a second element is known as cam.
• The second element is called a follower.
• The cam usually rotates at a constant speed and drives the follower whose motion depends upon the shape of the cam.
• Almost always the cam is driver and follower is driven.

Therefore, The rotating member is a cam which can also be called as the driver.

Important Points

Depending upon the shape and axis of motion, the following types of cam followers are used in practice:

• Pointed or knife-edge followers
• Roller followers
• Flat face followers
• Spherical followers

Explanation:

When the motion of the follower is along an axis away from the axis of the cam center, it is called off-set follower.

If the follower movement is a displacement from the cam centre then the follower is called as an offset follower, offsetting results in reduced forces and stresses.

The offsetting eccentricity should be in the direction to improve force components tending to jam the translating follower in its bearing guide and decrease the wear between follower and cam surface.