Cam is a mechanical device used to generate irregular motion of mechanical elements. The cams are used to convert the rotary motion into oscillatory motion or oscillatory motion into the rotary motion. The two links acts as an input member. The other links acts as an output membrane, which is called as a follower.
With direct contact, the cam transfers the motion to the follower. Cams is mainly used in the machine tools, internal combustion engines, textile weaving industries, printing control automatic machines etc.
Elements of cam:
- Cam is known as driver member
- Follower is known as driven member
- The one that supports the cam and guides the follower is known as frame.
Types of cam:
Cam are divided into two types they are
- According to the shape
- According to the follower moment
- According to the construction of the follower
According to the shape, it is further divided into six types they are
- Wedge or flat cams
- Radial or Disc Cams
- Spiral cams
- Cylindrical cams
- Conjugate cams
- Globoidal Cams
- Spherical cams
Wedge or flat cams:
- A wedge cam has a wedge and also has translational motion.
- The follower can either have translated or oscillation motion.
- To maintain a contact between the follower and cam, a spring is used.
Radial or Disc cams:
- The follower moves radially along with the center of rotation, is known as radial cam.
- Due to the simplicity and compactness the radial cams are very popular
- The follower oscillates about an axis parallel to the axis of rotation of the cam.
- In the spiral cam, groove is cut in the form of a spiral and is also known as face cam.
- The grove consists of teeth and they are meshed with a pin gear follower.
- From the axis of the cam, the follower velocity is proportional to the groove radial distance.
- Mainly the spiral cams are used in computer.
- Cylindrical cams are also known as drum cams or barrel cams.
- In the cam, the cylinder consists of a circumferential contour cut in the surface and the cylinder rotates about its axis.
- The follower motions are divided into two types:
1) Cam consists of a groove cut, as it is made on the surface of the cam and a positive oscillating motion is maintained by the roller follower.
2) Another type of cam is End Cam, in the end cam the end of the cylinder is a working surface.
- “Spring loaded” follower converts end to end or is parallel to the axis of the rotating cylinder.
- Conjugate cam is also known as double dis-cam. The discs are set together, plus the two rollers of a follower are in contact.
- The follower maintains a positive constraint.
- Conjugate cams are chosen when there is a requirement of low noise, low wear, high dynamic loads, high speeds and better control of the follower.
- Globoidal cams are divided into two types they are concave or convex type and surface type.
- To import motion to the follower a circumferential contour cut is made on the surface of rotation of the cam and they have an oscillatory motion.
- Globoidal cams are used at moderate speeds. The angle of oscillation of the follower is large.
- In the spherical cam, the follower oscillates about the axis perpendicular to the axis surface of rotation of the cam.
- In the spherical cam consists of a spherical surface which transmits motion to the follower.
According to the follower moment
- Rise – Return – Rise (RRR)
- Dwell – Rise – Return _ Dwell (D-R-R-D)
- Dwell – Rise – Dwell – Return – Dwell (D-R-D-R-D)
Rise – Return – Rise (RRR)
In the Rise- return – Rise, there is an alternate rise and return of the follower with no periodic form of dwells. The follower has a linear or an angular displacement.
Dwell – Rise – Return-Dwell (D-R-R-D)
In Dwell – Rise – Return – Dwell after a dwell there are rise and return of the follower. This type is used more normally than the Rise – Return – Rise type of cam.
Dwell – Rise – Dwell – Return – Dwell (D-R-D-R-D)
- Dwell – Rise – Dwell – Return – Dwell is the most commonly used cam.
- Cam dwelling is followed by dwell and it rises and returns successively.
- In the case of return of the supporter is by a fall. The motion is known as Dwell – Rise – Dwell.
According to the construction of the follower
Preloaded spring cam
Positive drive cam
Preloaded spring cam
The preloaded spring is used to make a contact between the follower and the cam
Positive drive cam
In the positive drive cam, the contact between the follower and the cam is maintained by a roller follower working in the groove of a cam. During normal working conditions, the follower does not move out of the groove. By using the conjugate cam, positive drive is obtained.
Rising surface of the cam is achieved by rise of a cam, and the cam must be returned by the force of gravity. This can also return due to the weight of the cam. There are certain limitations due to the uncertain behavior.
Classification of followers is done:
According to the shape
According to the movement
According to the location of the line of movement
According to the shape
Knife edge Follower
Mushroom Follower or Flat Faced follower
Spherical faced follower
Knife edge follower
- Knife edge follower is known as the end of the contacting follower has a “sharp knife edge”.
- The sliding motion must be taken between the cam surface and knife edge.
- The small contacting surface results in excess ware.
- The side thrust must exist between the guide and the follower.
- If the follower contacting end is a roller then it is known as the roller follower.
- The rolling motion must be takes place in between the cam and the roller.
- The ware must be critically reduced
- The side trust exists between the guide and the follower.
- We can observe the roller follower mainly when there is availability of more space in oil engines, stationary gas and aircraft engine.
Flat Faced or Mushroom Follower:
- If the contacting end of the follower is flat faced, then it is known as the flat face or mushroom follower.
- In this condition the side thrust between the guide and follower is reduced very much.
- Due to limited space in cam the flat faced followers are used to operate the automobile engine valves are used.
Spherical faced follower
- The follower connecting end is spherical, and then it is known as spherical faced follower.
- In order to minimize the stress that is developed by the flat faced follower, the spherical faced followers are used.
According to the motion of the follower, they are two types:
- Translating follower or reciprocating follower
- Rotating follower or oscillating follower
Translating follower or Reciprocating follower
The cam rotates uniformly when the follower reciprocates within the guides, it is known as translating follower or reciprocating follower.
Rotating follower or oscillating follower:
In the cam when the uniform rotary motion is converted into the determined oscillatory motion of the follower, it is known as the rotating follower or oscillating follower.
According to the path of motion of the follower:
If the line of movement of the follower passes through the center of rotation of the cam, it is known as radial follower.
Off – set follower:
If the line of movement of the roller follower is offset from the center of rotation of the axis then it is known as the off – set follower.
Terms used in the cam:
Base Circle: Base Circle is the smallest circle which is tangent to the cam profile which is drawn from the midpoint of rotation of a radial cam.
Pressure Angle: It is the angle between the normal to the pitch curve and the follower motion. In the design of the cam profile, the pressure angle is important. If the pressure angle is large then the reciprocating follower can jam its bearing.
Trace point: The trace point is a reference point on the follower and it is used as a pitch curve.
Pitch point: On the pitch curve it is a point which is has the maximum pressure angle.
Pitch curve: With the help of the trace points pitch curve is generated and the follower moves comparative to the cam.
Prime circle: Prime circle is a smallest circle drawn line to the pitch curve is known as prime circle.
Angle of Ascent: It is the angle through which the cam turns in the process of the follower rise.
Angle of Action: It is the total angle moved by cam during the time, between the beginning of the rise and the end of a return of the follower.
Angle of Descent: It is the angle through which the cam turns during the time the follower returns to the initial position.
Angle of Dwell: Angle of dwell is the angle through which the cam turns while the follower remains motionless at the highest or lowest situation.
Life or stroke: From lowest position to the topmost position maximum travel by the follower is known as stroke.
Types Motion of the follower:
- Uniform velocity
- Simple harmonic motion
- Uniform acceleration and retardation
- Cycloidal motion
Applications of cams:
In IC engine, the Exhaust values and inlet valves operate with the help of cam.
In automatic lathe machines, the feed mechanism is used
In weaving textile machineries, the cam are used
Paper cutting machine the cams are used
In clocks the cams are used
Advantages of Cams:
- Very long life
- Quiet Operations
- Low shock and acceleration
- High load carrying capacity
Disadvantages of cams:
- Rotary input is required
- Manufacturing of the cam must be more pertinent
click here to know more about: Basic Thermodynamics