Types of followers

Cam followers are different types they are classified according to :

1. Shape
2. Types of follower motion
3. Location of the line of movement

According to shape :

1. Knife-edge follower
2. Roller follower
3. Mushroom follower 

Let we check it out above follower in details :

• Knife-edge follower :

In knife-edge follower, the connecting end of the follower has a sharp knife-edge so that its called knife-edge follower.

This type of follower is quite simple in construction.

It produces great wear of the surface at the point of contact and considerable thrust exist so its use is limited.

• Roller follower :

In roller follower, the connecting end of the follower is a roller so that is called roller follower.

Wear rate is greatly reduced because of rolling motion between contacting surfaces of the cam and follower.

At low speed, the follower has a pure rolling action but at high speeds, some sliding also occurs.

Roller followers are commonly used where more space is available in the large stationary gas or oil engines and aircraft engines.

In case of a steep rise, a roller follower jams the cam and therefore it is not preferred.

• Mushroom follower :

A mushroom follower is also two types :

1. Flat-faced follower
2. Spherical follower

• Flat-faced follower :

In flat-faced follower connecting end of the follower is perfectly flat-faced so that is called flat-faced follower.

The thrust at the bearing exerted is less as compared to another follower.

In this follower, high surface stresses and wear are quite high due to deflection and misalignment.

This types of follower are mostly used in an automobile.

• Spherical follower :

In spherical follower connecting end of the follower is spherical in shape so its called spherical follower.

In flat-faced follower, high surface stress is produced to minimize these stress the follower is machined to spherical shape.

According to follower movement :

1. Reciprocating follower 
2. Oscillating follower 

• Reciprocating follower :

In this type, the cam rotates and the follower reciprocates or translates in the guides of the cam.

This is also called translating follower.

• Oscillating follower :

In this type, cam makes the rotary motion and follower is pivoted at the suitable point on the frame and oscillating as the cam makes a rotary motion.

According to the location of the line of movement :

• Radial follower :

In this type of follower, the line of movement of the follower passes through the centre of rotation of the cam. 

• Offset follower :

In this type of follower, the line of movement of the roller follower is offset from the centre of rotation of the cam.

You may also check different types of the cam.

Types of cam

Cams are classified according to the following terms :

• Shape
• Follower movement
• Manner of the constraint of the follower 

According to shape :

1. Wedge and flat cams
2. Radial or Disc cams
3. Spiral cams
4. Cylindrical cams
5. Conjugate cams
6. Globoid cams
7. Spherical cams

Now explain the above types of cams in details : 

• Wedge and flat cams :

A wedge cam has a wedge W has a translational motion.

The follower F can either translate or oscillate.

In that type of cam, spring is usually, used to maintain the contact between the cam and the follower.

The cam is stationary and the follower constraint or guide G causes the relative motion of the cam and the follower.

• Radial or Disc cams :

  

A cam in which the follower moves radially from the centre of rotation of the cam is known as a radial cam.

Radial cams are very popular due to their simplicity and compactness.

• Spiral cams :

A spiral cam is a face cam in which a groove is cut in the form of a spiral. The spiral groove consists of teeth which mesh with a pin gear follower. 

The use of such cam is limited as the cam has to reverse the direction to reset the position of the follower. It is mainly used in computers.

• Cylindrical cams :

In a cylindrical cam, a cylinder which has a circumferential contour cut in the surface rotates about its axis. For this cam follower motion can be two types :

• A groove is cut on the surface of the cam and a roller follower has a constrained oscillating motion.
• An end cam in which the end of the cylinder is the working surface. 

Cylindrical cams are also known as barrel or drum cams.

• Conjugate cams :

A conjugate cam is a double-disc cam, the two discs being keyed together and are in constant touch with the two rollers of a follower. 

Thus, the follower has a positive constraint. 

Such cam is preferred when the requirements are low wear, low noise, better control of the follower, high speed and high dynamic loads.

• Globoid cams :

A globoid cam can have two types of surfaces, convex or concave. 

A circumferential contour is cut on the surface of rotation of the cam to import the motion to the follower which has an oscillatory motion.

Such types of the cam are used in limited to moderate speeds and where the angle of oscillation of the follower is large.

• Spherical cams :

In spherical cam, the follower oscillates about the axis perpendicular to the axis of rotation of the cam.

This type of cam is in the form of a spherical surface.

According to follower movement :

• Rise-Return-Rise ( R-R-R)
• Dwell-Rise-Return-Dwell ( D-R-R-D )
• Dwell-Rise-Dwell-Return-Dwell ( D-R-D-R-D )

The motion of the followers is distinguished from each other by the dwells they have.

Now the question arises in your mind is what is dwell?

A dwell is zero displacements or the absence of motion of the follower during the motion of cam.

Now explain the above types of cams in details : 

• Rise-Return-Rise ( R-R-R ) :

In this type of cam, there is an alternate rise and return of the follower with no periods of dwells.

In this type of cam follower has a linear or an angular displacement.

• Dwell-Rise-Return-Dwell ( D-R-R-D ) :

In this type of cam there is rise and return of the follower after a dwell.

This type of cam are more frequently used than the R-R-R cam types.

• Dwell-Rise-Dwell-Return-Dwell ( D-R-D-R-D ) :

In this type of cam dwelling of the cam is followed by rise and return.

This type of cam is most widely used cam types.

According to manner of constraint of the follower :

1. Pre-loaded Spring Cam
2. Positive-drive Cam
3. Gravity Cam

Introduction of cam and Follower

In this article, we have to see some basic knowledge about the cam and follower and about cam mechanism. Let we know first what is cam?

A cam is a mechanical member used to impact desired motion to a follower by direct contact.   
                                                                   OR

Cam is the part of a machine in sliding or rolling contact with a rotating cam and given motion by it.

The cam may be rotating or reciprocating whereas the follower may be rotating, reciprocating or oscillating. Now the question may arise that what is a follower?

Cam drives the mating element in mechanical linkage of motion is called FOLLOWER.

There are many different types of the cam are widely used in automobile, automatic machines, internal combustion engine, machine tools, printing control mechanisms etc.

Cams are manufactured by die-casting, milling or by punch-press.

A cam and the follower combination belong to the category of a higher pair. 
In that mechanism :

• A driver member is known as the cam.
• A driven member is known as a follower.
• A frame that can support the cam and guides the follower.

Spur gear backlash

In this article, we have discussed the backlash of the spur gear. so let us know first 
What is the backlash ?

• Backlash is defined as the amount by which the width of tooth space exceeds the thickness of the engaging tooth measured along the pitch circle.

Backlash is the play a vital role in spur gear designing it plays between the missing teeth and it occurs only when teeth are in mesh.

Why provide backlash?

• Backlash compensates for machining errors 
• Backlash compensates for thermal expansion of teeth.
• Backlash prevent the mating teeth from jamming together.

Methods to provide backlash :

• The centre distance between mating gears is slightly increased.
• The teeth of the gear are cut slightly thinner.

The magnitude of backlash is depended upon the diametral pitch or module and the centre distance.

The magnitude of backlash is very small for gear trains used in precision equipment and instruments.

The backlash and variation in centre distance have no effect on tooth action or velocity ratio.

What is rigid body

What is Rigid body?

Answer :

A body is said to be rigid if, under the action of forces, it does not suffer any distortion.

Another way to said that the distance between any two points on the body remains constant.

What is Kinematics and Dynamics

What is Kinematics?

It deals with the relative motion of different parts of a mechanism without taking into consideration the forces producing the motions.

Kinematics is the geometry of motion.

What is Dynamics?

It involves the calculations of forces impressed upon different parts of the mechanism.

Dynamics is geometry + physics of motion.

The forces can be either static or dynamics.

Dynamics is further subdivided into two groups :

• Kinetics
• Statics

Kinetics is the study of forces when the body is in motion. 

Statics is the study of forces when the body is stationary.

Terminology of Spur Gear

Pinion : A pinion is a smaller of the two mating gears.

Gear : A gear is the larger of the two mating gears.

Velocity Ratio : Ratio of angular velocity of the driving gear to the angular velocity of the driven gear. It is also called speed ratio.

Transmission Ratio : Ratio of the angular speed of the first driving gear to the angular speed of the last driven gear in a gear train.

Pitch Surface : The pitch surface of the gears are imaginary planes, cylinders or cones that roll together without slipping.

Pitch Circle : The pitch circle is the curve of intersection of the pitch surface of revolution and the plane of rotation. It is and imaginary circle that rolls without slipping with the pitch circle of a mating gear.

Pitch Circle Diameter : The pitch circle diameter is the diameter of the pitch circle. The pitch circle diameter is denoted by d.

Pitch Point : It is a point on the line of centres of two gears at which two pitch circles of mating gears are tangent to each other.

Top Land : It is the surface of the top of the gear tooth.

Bottom Land : It is surface of the gear between the flanks of adjacent teeth.

Involute : An involute is a curve traced by a point on a line as the line rols without slipping on a circle.

Base Circle : The base circle is and imaginary circle from which the involute curve of the tooth profile is generated. The base circle of two mating gears are tangent to the pressure line.

Addendum Circle : The addendum circle is an imaginary circle that borders the tops of gear teeth in the cross section.

Addendum : The addendum is radial distance between pitch and addendum circle. It indicates the height of the tooth above the pitch circle.

Dedendum Circle : The dedendum circle is an imaginary circle that borders the bottom of spaces between teeth in the cross section. It is also called root circle.

Dedendum : The dedendum is the radial distance between pitch and the dedendum circles. It indicates the depth of the tooth below the pitch circle.

Clearance : The clearance is the amount by which the dedendum of a given gear exceeds the addendum of its mating tooth.

Face of tooth : The surface of gear tooth between the pitch cylinder and the addendum cylinder is called the face of tooth.

Flank of tooth : The surface of the gear tooth between the pitch cylinder and the root cylinder is called flank of tooth.

Face width : Face width is the width of the tooth measured parallel to the axis.

Fillet Radius : The radius that connects the root circle to the profile of the tooth is called fillet radius.

Tooth Space : The width of space between two adjacent teeth measured along the pitch circle is called tooth space.

Working Depth : The working depth is the depth of engagement of two gear teeth that is sum of their addendums.

Whole Depth : The whole depth is total depth of the tooth space that is sum of the addendum and dedendum.

Whole depth = Working depth + clearance

 

Centre Distance : The centre distance is the distance between centres of pitch circles of mating gears.

Pressure angle : The pressure angle is the angle which the line of action makes with the common tangent to the pitch circles. It is also called angle of obliquity. It denoted by α.