AM221 - Radial Cam and Follower

 For procedures, see your mechanical laboratory manual.

Title: Radial Cam and Follower

Aim

To record the kinematics properties of various radial cams.

Theory

In mechanical engineering, engineers often use a higher pair links mechanism that is renowned as Cam and Follower Mechanism. This pair of higher links are used to move links spontaneously or periodically.

Although, cam and follower mechanisms are also used by engineers for ensuring zero or minimum degree of error. The device that is known as Cam in the 3rd century was devised by Hellenistic water-driven automata.

Alongside, that device was found in the 4th century in Al-jazari design. The Cam and Follower Mechanism is mostly used in the IC engines for driving the valves. Apart from that, the mechanism is often used by engineers as a part of the I.C.Es timing system.

Cam

A cam is a reciprocating, oscillating, or rotating body which imparts reciprocating or oscillating motion to a second body, called the follower, with which it is in contact. A cam is generally a disc or a cylinder mounted on a rotating shaft, which gives a special motion to a follower, by direct contact. The shape of the contacting surface of the cam is determined by the desired motion and the profile of the follower.

Cam-follower mechanisms are particularly useful when a simple motion of one part of a machine is to be converted to a more complicated desired motion of another part, one that must be accurately timed concerning the simple motion
and may include periods of dwells.

Cams are essential elements in automatic machine tools, textile machinery, sewing machines, printing machines, and many others. If the follower is not restrained by a groove on the cam, a spring is necessary to keep the follower in contact with the cam. Cam systems can replace relatively complicated linkages in achieving desirable motion cycles. A cam timer is similar and was widely used for electric machine control (an electromechanical timer in a washing machine being a common example) before the advent of inexpensive electronics, microcontrollers, integrated circuits, programmable logic controllers, and digital control. When multiple cams are incorporated within a single shaft it is called a camshaft.

In all cam systems, it is important that the follower is always in contact
and following the motion of the cam. This is achieved in several
ways including the following.

• Gravity
• Using a mechanical constraint system, i.e. groove
• Using a spring force
• Using pneumatic or hydraulic force

Cams are made in a variety of forms, including

• A rotating disk or plate with the radial required profile
• A reciprocating wedge of the required shape
• A cylindrical barrel cam with a follower groove cut in the diameter
• A cylinder with the required profile cut in the end (end cam)

Types of Cam

There are various types of cams available.

Disk or Plate Cam

The disk (or plate) cam has not regular contour to transmit a specific motion to the follower.

Cylindrical Cam

The cylindrical cam has a groove in a cylindrical surface and the follower runs on the cylindrical surface parallel to the axis of the cylinder.

Translating Cam

Translating cam has a grooved or contoured plate and its follower oscillate in the face of the plate. The groove or the contour has specified the motion of the follower.

Wedge Cam

The wedge cam has an angled flat regular contour to impart a specific motion of the follower.

Spiral Cam

The spiral cam has a half-circular or a spiral shaping grooved contour, the cam moves in reciprocating motion and the follower moves vertically to the axis of the cam. 

Heart-shaped Cam

This type of cam looks like an asymmetric heart. It is mainly used to return a shaft to hold the cam to a set position by its pressure from a roller.

Follower

A follower is a rotating or an oscillating element of a machine that follows the motion of a cam by direct contact.

If a cam moves in reciprocating motion the follower moves in vertically concerning the axis of the cam. This part of the machine is mainly following the cam which can be reciprocating or oscillating in motion. It converts the rotary motion of the cam into reciprocating or oscillating motion.

The motion of the follower is restricted to a pre-determined pattern by a guide. The

follower maintains contact with the cam through the force of gravity or by a spring.

The total range of movement produced by the cam is called the stroke. The range of movement of the follower will depend on the distance from the shaft supporting the cam to the upper and lower points of the rotation circle.

Types of Follower

There are various types of followers.

Knife-edge Follower

This type of follower has a sharp area of contact with the cam. This is the simplest among all of the followers and these kinds of followers are not in use in the case of fast application, because of its sharp edge.

Roller Follower

This type of follower is mainly used in high-speed operation because it has smooth contact with the surface. This type of follower has less wear and tear as compared to the other followers.

Flat-faced Follower

This type of follower looks like a flat surface with an irregular cam. This type of cam is used when the space is limited and this follower can resist more side thrust. This follower can also be used in a precision application.

Spherical Follower

This type of follower has a curved but regular follower as well as a cam. This is a modification of a flat-faced follower.

Radial Follower

In this type of follower, the line of movement passes through the center of the camshaft. Mainly the movement of the follower is in line. The follower is in a reciprocating motion.

The diagram is the same as knife-edge follower.

Offset Follower

In this type of follower, the movement of the axis of the follower is not collinear with the cam axis.

Working Principle of Cam and Follower

The working principle of Cam and Follower depends on the mechanism of the combination of both Cam and Follower.

Cam Mechanism

Cam is a mechanical component that is a rotating circle or eclipse about the minor axis of the Follower. Hence it can be explained easily that Cam is a mechanical component that transmits reciprocating, oscillating, or linear motion to Follower.

Cam’s shape is usually an oval or an imperfect circle or an eclipse. If an engineer considers an oval-shaped Cam then he or she can see the movements which will form the outer bulge, which is periodic to its locus. This outer bulge is very useful and effective for works that are periodic mechanical. There are two types of Head Cams. The first is Single Head Cam and the second is Multiple Head Cam.

Cam is Rotating about minor axis or respect to Follower.

Follower Mechanism

A follower is a mechanical component concerning which, the Cam rotates in an oscillatory or circular motion. Follower inhibits the push and pulls of the Cam. A follower is used to transfer the motion to the required machine part. The Follower rotates in an oscillating or circular arc.

The mechanism for Cam and the mechanism for Follower depend upon each other so that the main mechanism of Cam and Follower.

The Terminology of a Cam

Cam Profile - It is the surface area of a cam where the follower touches.

Base Circle - It is the smallest circle of a cam profile drawn from the center of rotation of the cam.

Trace Point - By this point, we can trace the cam profile.

Pitch Curve - This curve is generated if we assume the cam is fixed and the tracepoint of the follower moves around the cam.

Pressure Angle - It is formed between normal to the pitch curve and line of motion of the follower.

Pitch Point - At this point the pressure angle is maximum.

Pitch Circle - It is the circle which passes through the pitch point.

Prime Circle - This is a circle that is drawn tangentially to the pitch curve and concentric to the base circle.

Importance of Cam and Follower

In the field of mechanical engineering, the Cam-follower mechanism plays a significant role in achieving even distribution of forces in a single machine component. By attaching a cylindrical roller in a machine component spontaneous movement can be achieved by an engineer. Cam follower can be used in a machine component regardless of the shape and size of the nut. Apart from that, varieties of linear motions can be found by utilizing the mechanism. Moreover, due to higher thickness as compared to other bearings Cam follower mechanism can absorb a higher amount of shock that increases the mechanical efficiency of a machine component.

Furthermore, the mechanism is entirely versatile in that it can be used in a soda machine or also in an aircraft application. Besides, the mechanism is also used in the conveyor belt. In the case of engines, bearing the load of a camshaft can easily be devised by utilizing the fundamental approach of a crankshaft bearing. Although, flat followers are used by engineers to operate the valves of an engine whereas roller followers are used by engineers in oil and stationary engines. This type of preference occurred due to more availability of space of roller followers.

Applications of Cam and Follower

There are several applications of the Cam and Follower mechanism. 

• Internal Combustion Engine to close and open the outlet valve and intake valve.
• Automated Types of machinery, Cam and Follower are used in different parts which are automated in motion.
• In Hydraulic Systems, the main mechanism is Cam and Follower mechanism.
• In that case, the mechanism is dependent on the fluid pressure.
• In Printing Machinery, the mechanism of Cam and Follower helps the screen to be printed. The push helps to take the position where the printing will be done and the pull helps to print on that.
• In Textile Types of machinery, the mechanism of Cam and Follower helps to stitch clothes by a push and pull to move the Maku.
• Screw pieces of machinery.
• Gear-Cutting Machineries.
• Wall-Clock.
• Automatic Lathe Machine.

References

1. Manual of Engineering Drawing (Fifth Edition), 2020.
2. N. Gokarneshan, B. Varadarajan, C.B. Senthil Kumar, in Mechanics and Calculations of Textile Machinery, 2013.
3. David J. Spencer, in Knitting Technology (Third Edition), 2001.
4. Cam, wikipedia.org.
5. Cam and Follower, learnmechanical.com.
6. Kinematics of Machines Prof. A.K. Mallik Department of Mechanical Engineering, Indian Institute of Technology, Kanpur.
7. Introduction to Cam Design, Department of Mechanical Engineering, University of Minnesota.
8. Cam and Follower Mechanism, WJEC.