Introduction to Classifications of Cams and Followers

Definition

A Cam and Follower mechanism is a mechanical linkage consisting of a rotating or oscillating element (the Cam) that imparts a specific motion to a second element (the Follower) through direct contact. It is widely used to convert rotary motion into reciprocating or oscillating motion in machines like internal combustion engines, textile machinery, and automated assembly lines.

Main Content

1. Classification of Cams

Cams are primarily classified based on their shape and the path of the follower.

• Radial or Disc Cams: The follower moves in a direction perpendicular to the axis of the cam rotation. The cam profile is machined on the periphery of the disc.
• Cylindrical or Barrel Cams: The follower moves in a direction parallel to the axis of the cam rotation. The follower rides in a groove cut into the surface of a cylinder.

  Radial Cam          Cylindrical Cam
    __                ____________
   /  \              |   ______   |
  | (O)| < Follower  |  /      \  | < Follower
   \__/              |____________|

2. Classification of Followers by Surface Shape

This classification refers to the geometry of the follower end that touches the cam.

• Knife-Edge Follower: The contacting end is a sharp knife edge. It offers the most flexibility in cam design but experiences high wear due to the small contact area.
• Roller Follower: The contacting end is a small roller. This is widely used in high-speed applications because it replaces sliding friction with rolling friction.
• Flat-Faced Follower: The contacting end is a flat surface. It is excellent for lifting heavy loads but requires a large contact area.
• Spherical-Faced Follower: The contacting end is slightly curved. This combines the benefits of the flat face and the roller, often used to prevent edge contact.

3. Classification of Followers by Motion

This refers to how the follower moves relative to the cam axis.

• Radial (In-line) Follower: The line of motion of the follower passes through the center of the cam rotation axis.
• Offset Follower: The line of motion of the follower is offset by a certain distance from the center of the cam rotation axis. This is often used to reduce side thrust during the power stroke.

Working / Process

1. The Input Phase (Rotation)

• The Cam is mounted on a rotating shaft (the camshaft) driven by a motor or engine.
• As the cam rotates, its irregular profile (the "lobe") pushes against the follower, forcing it to move according to the cam's geometric design.

2. The Transmission Phase (Contact)

• The Follower maintains constant contact with the Cam through a spring mechanism or gravity.
• The shape of the cam profile dictates the velocity and acceleration of the follower at every degree of rotation.

3. The Output Phase (Execution)

• The Follower moves back and forth (reciprocation) or pivots (oscillation).
• This motion is transmitted to the machine component (e.g., opening an intake valve in a car engine at a precise moment).

Advantages / Applications

• Precision Timing: Allows for complex, irregular motion sequences that gears or linkages cannot easily produce.
• Compact Size: Highly efficient in space-constrained machinery like internal combustion engines.
• Reliability: Simple construction with very few moving parts ensures high durability in automated manufacturing lines.

Summary

A Cam and Follower mechanism is a fundamental kinematic system that translates rotary input into controlled follower output. Cams are classified by shape (Radial vs. Cylindrical), while followers are classified by their contact geometry (Knife, Roller, Flat, Spherical) and motion path (In-line vs. Offset).

Important terms to remember: - Cam Profile: The actual physical surface shape of the cam. - Base Circle: The smallest circle that can be drawn tangent to the cam profile. - Trace Point: The theoretical point on the follower that determines the cam profile. - Pressure Angle: The angle between the direction of follower motion and the normal to the pitch curve.