Construction of Cam Profile

Definition

A cam profile is the actual physical boundary or contour of a cam that determines the specific motion of the follower. The construction of a cam profile involves plotting the radial distances of the cam surface at various angular positions to achieve a desired displacement program (motion cycle) for the follower.

Main Content

1. Kinematic Requirements

The cam profile design is dictated by the follower's displacement, velocity, and acceleration requirements.
Common motion types include Simple Harmonic Motion (SHM), Uniform Velocity, and Cycloidal motion to ensure smooth operation at high speeds.

2. The Base Circle

The base circle is the smallest circle that can be drawn to the cam profile from the center of cam rotation.
It determines the overall size of the cam; a larger base circle results in a gentler pressure angle, which reduces wear on the mechanism.

3. Trace Point and Pitch Curve

The trace point is the theoretical point on the follower (e.g., the center of a roller follower) that traces the path of motion.
The pitch curve is the path generated by the trace point as the cam rotates. The actual cam profile is then constructed by offsetting the pitch curve by the radius of the roller.

       Follower
          |
        ( O )  <-- Trace Point
          |
    --------------
   /              \
  |  Cam Profile   |
   \              /
    --------------

Working / Process

1. Defining the Displacement Diagram

Plot the follower displacement (y-axis) against the cam angle (x-axis) for one full rotation (360°).
This diagram visualizes the Rise, Dwell, and Return (RDR) phases of the follower.

2. Constructing the Pitch Curve

Draw the base circle and divide it into angular segments corresponding to the displacement diagram.
Mark the radial positions of the follower center on these segments to create the locus of the trace point.

3. Constructing the Final Profile

For a roller follower, draw a series of circles with the roller radius centered along the pitch curve.
Draw a smooth tangent curve that touches all these circles; this resulting outer boundary is the actual manufactured cam profile.

Advantages / Applications

Allows for complex, non-linear mechanical movements that are difficult to achieve with linkages.
Widely used in Internal Combustion (IC) engines to control the timing of intake and exhaust valves.
Essential in automated machinery, such as printing presses, packaging machines, and textile looms, to synchronize repetitive operations.

Summary

The construction of a cam profile is the engineering process of shaping a cam to produce precise follower motion. By translating a displacement diagram into a physical contour through the determination of the base circle, pitch curve, and follower offset, engineers ensure smooth kinematic performance. Key terms to remember include Base Circle, Pitch Curve, Trace Point, Pressure Angle, and Dwell.