In the field of mechanical engineering, a cam is a machine element that is typically made in the form of a circular disc or cylinder. It has an irregular shape on its surface that is specially designed to impart a prescribed motion to a follower, which is a machine element that is in contact with the cam’s surface.
The follower moves relative to the cam’s surface in accordance with the profile of the cam. The motion of the follower can be used to perform a variety of functions, such as controlling the opening and closing of valves in engines, providing motion for textile machinery, and controlling the motion of robotic limbs.
The cam and follower mechanism is commonly used in applications where a specific motion is required, and it is desirable to have a compact and simple mechanism to achieve that motion. Cam mechanisms are known for their precision, repeatability, and their ability to generate complex motion profiles.
The follower can take many forms, such as a roller, a flat-faced follower, or a mushroom-shaped follower. The choice of follower type depends on the desired application and the motion required. The follower is typically mounted on a shaft and may have additional elements, such as springs or hydraulic cylinders, to maintain proper contact with the cam surface.
A cam is a machine element that is commonly used to convert rotational motion into linear motion. It is a component that consists of an eccentric or non-circular shape mounted on a rotating shaft. The shape of the cam profile determines the movement of the follower, which is a component that moves in contact with the cam surface.
The main use of a cam is to create reciprocating or oscillating motion in a follower, which can then be used to perform a variety of functions. Cams are used in a wide range of mechanical devices, including engines, pumps, and automation equipment. Some common applications of cams include opening and closing valves, controlling the position of machine components, and driving conveyor systems.
Cams can also be used to create more complex motion patterns. For example, a cam may be designed to generate a sinusoidal motion, which can be used to produce a smooth, continuous motion in a machine component. Cams can also be used in combination with other mechanical components, such as gears and linkages, to create more complex mechanisms.
Recall the Classification of Followers according to (Wrong video) i. the Surface in Contact ii. The Motion of Follower iii. Path of the Motion of the Follower
The Surface in Contact:
Followers can be classified based on the shape of the contact surface between the cam and the follower. Examples include flat-faced followers, roller followers, mushroom or convex followers, and knife-edge or pointed followers.
ii. The Motion of Follower:
Followers can also be classified based on the motion they experience while following the cam profile. Examples include translating followers, oscillating followers, and rotating followers.
iii. Path of the Motion of the Follower:
Followers can also be classified based on the path they take while following the cam profile. Examples include radial or disc cam followers, cylindrical or axial cam followers, and conical cam followers.
Understanding the different types of followers is important when designing a cam-follower system, as different types of followers are suited for different applications. The choice of follower type can depend on factors such as the load and speed of the system, the desired accuracy of motion, and the amount of wear on the system.
The classification of cams can be based on different factors, such as the shape of the cam, the follower motion, the surface in contact, and the number of followers. One of the most common classifications of cams is based on the shape of the cam.
- Radial or Disc Cam: A radial or disc cam is a type of cam that has a flat or curved disc-shaped surface. The follower moves in a radial direction in contact with the surface of the cam. Radial cams are commonly used in engines and machines that require uniform motion.
- Cylindrical Cam: A cylindrical cam is a type of cam that has a cylindrical surface. The follower moves in a direction parallel to the axis of the cam. Cylindrical cams are commonly used in machines that require reciprocating or oscillating motion.
Other types of cams based on the shape include grooved cams, wedge cams, and barrel cams.
Cams can also be classified based on the number of followers they have, such as single-dwell cams and double-dwell cams. Single-dwell cams have one follower, while double-dwell cams have two followers.
The classification of cams based on the surface in contact is typically based on the shape of the follower. For example, flat-faced followers are used with flat cams, roller followers are used with cylindrical cams, and spherical-faced followers are used with grooved cams.
The classification of cams based on the motion of the follower includes translating, oscillating, and rotating followers. Translating followers move in a straight line, oscillating followers move back and forth in an arc, and rotating followers move in a circular path.
Recall the Following terms used in Radial Cams i. Base circle ii. Trace point iii. Pressure angle iv. Pitch point and Pitch circle v. Pitch curve vi. Prime circle vii. Lift or stroke
In the design of radial cams, several key terms are used to describe the geometry and motion of the cam and its follower. Some of the important terms are:
- Base circle: It is the smallest circle that can be drawn tangent to the cam profile. It is used as a reference for other geometric features of the cam.
- Trace point: It is a point on the follower that contacts the cam profile during operation. The path of the trace point is determined by the shape of the cam profile.
- Pressure angle: It is the angle between the direction of the follower motion and the direction of the force between the follower and the cam. A smaller pressure angle is desirable, as it reduces the side thrust on the follower and the wear on the cam.
- Pitch point and pitch circle: The pitch circle is a reference circle that is used to define the angular position of the cam. The pitch point is a point on the cam profile that lies on the pitch circle. The pitch circle is used to determine the motion of the follower.
- Pitch curve: It is the locus of the pitch point as the cam rotates. The shape of the pitch curve determines the motion of the follower.
- Prime circle: It is a circle that passes through the pitch point and is tangent to the follower. The prime circle is used to determine the lift or stroke of the follower.
- Lift or stroke: It is the maximum displacement of the follower from its rest position. The lift is determined by the shape of the cam profile and the size of the prime circle.
i. Rise and Return:
Rise is the linear upward movement of the follower from its lowest position to its highest position, as it follows the profile of a rotating cam or similar device. Return is the linear downward movement of the follower from its highest position back to its lowest position, also following the profile of the cam. The rise and return of the follower are usually symmetric and occur at the same rate.
Dwell is the period of time during which the follower remains stationary at its highest position, without any upward or downward motion. It is often designed into a cam profile to provide a period of rest or to allow for some action to occur while the follower is stationary. The duration of the dwell can be adjusted by changing the shape of the cam profile.
Define following angles for Cam Rotation: i. Angle of ascent and Descent ii. Angle of dwell and action
In the design of a cam and follower mechanism, the angular displacement of the cam is an important parameter. There are various angles associated with the rotation of the cam that are used in the analysis and design of cam mechanisms.
Angle of Ascent and Descent:
- The angle of ascent is the angle through which the cam rotates during the rise of the follower. It is the angle between the position of the cam when the follower starts to rise and the position of the cam when the follower reaches the maximum lift. The angle of descent is the angle through which the cam rotates during the return of the follower. It is the angle between the position of the cam when the follower starts to return and the position of the cam when the follower reaches its lowest point.
Angle of Dwell and Action:
- The angle of dwell is the angle through which the cam rotates during the period of maximum lift, during which the follower remains stationary. It is the angle between the position of the cam at the end of the rise and the position of the cam at the start of the return. The angle of action is the angle through which the cam rotates during the time in which the follower moves from the lowest position to the highest position. It is the sum of the angle of ascent and the angle of descent.
In cam design, these angles are important to ensure that the cam and follower operate smoothly and without impact or excessive wear. They are also used to calculate the velocity and acceleration of the follower and to determine the maximum contact stress between the cam and follower.
In cam design, it is important to analyze the follower motion to ensure it operates smoothly and efficiently. The follower motion is described by a set of derivatives that provide information on the velocity, acceleration, jerk, and snap of the follower at any given point in time.
The first derivative of the follower displacement is velocity, which provides information on the rate at which the follower is moving. The second derivative of displacement is acceleration, which indicates the rate at which the follower’s velocity is changing. The third derivative is jerk, which represents the rate of change of acceleration. Finally, the fourth derivative is snap, which indicates the rate of change of jerk.
By analyzing these derivatives, engineers can determine the ideal cam shape and cam-follower arrangement that will provide the desired motion profile for the follower. For example, minimising jerk and snap can reduce the wear and tear on the follower and other mechanical components, resulting in longer service life and more reliable operation.
Recall Mean Average Velocity of Follower
In mechanical systems that involve cams and followers, the velocity of the follower is an important parameter to determine the smooth operation of the system. One way to analyze the velocity of the follower is by calculating the mean average velocity of the follower during its displacement.
The mean average velocity of the follower is the average value of the velocity of the follower over a specific displacement. It is calculated by dividing the total displacement of the follower by the time taken for the follower to travel that distance.
In mathematical terms, the mean average velocity of the follower can be expressed as:
Vmean = (s2 – s1) / (t2 – t1)
where Vmean is the mean average velocity of the follower, s1 and s2 are the initial and final displacements of the follower, and t1 and t2 are the times taken for the follower to travel these displacements.
By calculating the mean average velocity of the follower, the designer can ensure that the follower is moving at a uniform and smooth speed, which can prevent any sudden jolts or jerks in the system.
Draw Cam Profile for the following Follower motions i. When moving with Uniform Velocity ii. When moving with Uniform Acceleration and Retardation
The cam profile is the shape of the cam that determines the motion of the follower. The shape of the cam must be designed in such a way that it produces the desired motion of the follower. The shape of the cam is determined by the displacement, velocity, and acceleration of the follower.
The follower motion can be of various types, and based on the type of motion, the cam profile can be designed. The two common types of follower motion are when it moves with uniform velocity and when it moves with uniform acceleration and retardation.
i. When moving with uniform velocity:
When the follower moves with uniform velocity, it moves at a constant speed throughout the motion. In this case, the cam profile is usually designed to have a constant slope. The slope of the cam profile is chosen such that it provides a constant velocity to the follower. The cam profile has a rise and a return, and the angle of ascent and descent are usually the same.
ii) When moving with uniform acceleration and retardation:
When the follower moves with uniform acceleration and retardation, it has a variable velocity throughout the motion. In this case, the cam profile is usually designed to have a curved slope. The cam profile has a rise, dwell, and return. The angle of ascent and descent are usually the same, and the angle of dwell and action are usually different. The cam profile is designed to provide the desired acceleration and retardation to the follower.
To draw the cam profile, the displacement, velocity, and acceleration of the follower are first determined. The displacement is then plotted on the vertical axis, and the angle of rotation of the cam is plotted on the horizontal axis. The slope of the cam profile is determined by the velocity, and the curvature is determined by the acceleration. Once the cam profile is drawn, it can be used to manufacture the cam and follower assembly.