Cams

A cam is a mechanical member used to impart desired motion to a follower by direct contact. Complicated output motions that are otherwise difficult to achieve can easily be produced with the help of cams.

cam animation
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Cams are wide utilized in automatic machines, combustion engines, machine tools, printing management mechanisms, and so on. They are factory-made sometimes by the die-casting, edge or by punching press.
A cam and also the follower combination belong to the class of upper pairs. Necessary parts of a cam mechanism are:
• A driver member referred to as the cam.
• A driven member is known as a follower.
• A-frame that supports the cam and guides the follower.

Cams are classified according to:

  1. Shape
  2. Follower movement
  3. Manner of the constraint of the follower.

Classification

According to shape

1.Wedge cams

cam

A wedge cam has a wedge W which, in general, has a translational motion. The follower F can either translate or oscillate. A spring is usually used to maintain contact between the cam and the follower.

2. Radial or disc cams

A cam within which the follower moves radially from the centre of rotation of the cam is understood as a radial or a disc cam. Radial cams are extremely popular owing to their simplicity and compactness.

disc cams

According to follower movement

The motions of the followers are distinguished from each other by dwells they have. A dwell is the zero displacement or the absence of motion of  the follower during the motion of the cam.

Cams are classified according to the motions of their followers as:

Rise-Return-Rise(R-R-R)

RRR

In this, there is an alternate rise and return of the follower with no period of dwells. It has a very limited use in the industry. The follower has an angular displacement

Dwell-Rise-Return-Dwell(D-R-R-D)

DRRD

In such type of a cam, there is a rise and return of the follower after a dwell. This type is used more frequently than the R-R-R type cam.

Dwell-Rise-Dwell-Return-Dwell(D-R-D-R-D)

DRDRD

This cam is the most widely used cam. The dwelling of the cam is followed by rise and dwell and subsequently by the return and dwell as shown.

According to Manner of Constraint of the Follower

To reproduce precisely the motion transmitted by the cam to the follower, the 2 must stay involved in the least speeds and in the least times. The cam is classified consistent with the style within which this is often achieved.

1. Pre-Loaded Spring Cam: A pre-loaded compression spring is used to keep the contact between the cam and the follower. 

2. Positive drive Cam: In this type, constant touch between the cam and the follower is maintained by a roller follower operating in the groove of a cam. The follower cannot exit this groove underneath the conventional operating operations. An unnatural or positive drive is additionally obtained by the utilization of a conjugate cam.

3. Gravity Cam: If the rise of the cam is achieved by the rising surface of the cam and the return by the force of gravity or due to the weight of the cam, the cam is known as a gravity cam. However, these cams are not preferred due to their uncertain behavior. 

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