A cam and follower mechanism is a type of mechanical device that converts rotary motion into linear motion. It consists of a cam, which is a rotating disk or cylinder with an irregular shape, and a follower, which is a lever or other object that rides along the surface of the cam. The cam pushes or pulls the follower as it rotates, creating a specific motion pattern. Cam and follower mechanisms are widely used in various machines and systems, such as valves, engines, pumps, door locks, stamping machines, etc.

Cams can have different shapes and profiles, depending on the desired output motion of the follower. Some of the common types of cams are disk or plate cams, wedge or flat cams, spiral cams, cylindrical or barrel cams, heart-shaped cams, translating cams, snail drop cams, conjugate cams, globoidal cams, and spherical cams. Each type of cam has its own advantages and disadvantages, and can produce different types of follower motions, such as rise, dwell, return, or oscillation.

Followers can also have different shapes and designs, such as rollers, levers, slides, or knife edges. The shape of the follower affects the contact stress and friction between the cam and the follower. The follower can be constrained by gravity, springs, or positive drive. Gravity followers rely on the weight of the follower to maintain contact with the cam. Spring followers use a spring force to keep the follower in contact with the cam. Positive drive followers use a mechanical linkage or a groove to ensure positive engagement with the cam.

Follower Shape Specification

There are different types of cam follower shapes and their usages, advantages or disadvantages depend on the design and application of the cam mechanism. Some of the common types of cam follower shapes are:

Roller follower: A roller follower has a cylindrical shape that rolls on the cam surface. It reduces friction and wear between the cam and the follower, and provides smooth and continuous motion. However, it may have problems with alignment and stability, especially at high speeds or heavy loads.

Spherical follower: A spherical follower has a spherical shape that slides on the cam surface. It can accommodate angular misalignment and radial displacement between the cam and the follower, and can operate in any direction. However, it has more friction and wear than a roller follower, and may require lubrication and maintenance.

Knife-edge follower: A knife-edge follower has a sharp edge that slides on the cam surface. It is simple and inexpensive to manufacture, and can follow complex cam profiles. However, it has high friction and wear, and may cause noise and vibration.

Flat-faced follower: A flat-faced follower has a flat surface that slides on the cam surface. It can withstand high axial forces and loads, and can follow cams with abrupt changes in profile. However, it also has high friction and wear, and may require lubrication and maintenance.

Cam Profile Specification

The profile of the cam is defined by specifying the extreme critical positions of the follower using position, velocity, acceleration, and jerk. These parameters are used to determine the shape and size of the cam, as well as the motion characteristics of the follower.

The position of the follower is the distance between its center and a reference point on the cam. The position determines the displacement of the follower from its initial position. The velocity of the follower is the rate of change of its position with respect to time. The velocity determines the speed of the follower along its path. The acceleration of the follower is the rate of change of its velocity with respect to time. The acceleration determines the force required to move the follower. The jerk of the follower is the rate of change of its acceleration with respect to time. The jerk determines the smoothness or roughness of the follower motion.

The extreme critical positions of the follower are the points where its position reach the maximum or minimum values. . The cam profile can be obtained by connecting these points with suitable curves, such as circular arcs, polynomials, or splines.

Fundamental Law of Cam Design

The fundamental law of cam design is that the follower motion must be continuous and smooth, without any abrupt changes in velocity or acceleration. This is because any discontinuity in the follower motion would cause impact, vibration, noise, wear and tear, and reduced performance of the cam-follower system. To ensure smooth follower motion, the cam profile must be designed with certain geometric constraints, such as curvature, pressure angle, and contact stress. The cam profile can be generated by various methods, such as graphical, analytical, or numerical techniques, depending on the type and complexity of the follower motion desired.

The profile of the cam is divided into regions of rise, dwell and fall, which correspond to the portions of the cam rotation where the follower moves up, stays at the same level, or moves down. For example, a cam may have a rise region for 20 degrees of rotation, followed by a dwell region for 40 degrees, and then a fall region for 300 degrees. To ensure smooth and continuous motion of the follower, and to avoid violating the fundamental law of cam design, the position function that describes the rise or fall region must be either a polynomial function, a harmonic function, or a combination of both. A polynomial function is a function that involves only powers of the independent variable, such as x^2 or x^3. A harmonic function is a function that involves trigonometric functions, such as sin(x) or cos(x). The potential combination of harmonics and polynomials enables a vast array of possible motions, speeds, and accelerations.

Cam Specification Example

Watch Professor Cummin’s detailed cam-follower example below.

Cam Specification in CAD

Below is a brief tutorial on defining the profile of a cam using the built in cam designer in the Solidworks toolbox. Other CADsoftware have similar features to support cam and follower design.