Cam and Follower | Definition , types , Nomenclature Of Cam
Cam is a mechanical element which is used to deliver the reciprocating or oscillating motion to another machine element known as follower. Cam and follower is a type of assembly, both works together in any machine element. Cam and followers are the example of higher pair due to the line contact between them. Some complicated motions are easily achieved by using cams and followers which are difficult to achieve. We can say that the cam and followers are the most important part of the mechanisms. The cams and follower combination is mostly used in internal combustion engines for operating inlet and exhaust valves, machine tools, printing control mechanism so on. They are generally manufactured by using die casting, milling and by punching.
A cam is a rotating or sliding piece in a mechanical linkage that drives a mating component known as a follower. From a functional viewpoint, a cam-and-follower arrangement is very similar to the linkages. The cam accepts an input motion (rotary motion or linear motion) and imparts a resultant motion (linear motion or rotary motion) to a follower.
Cam profile: Cam profile is outer surface of the disc cam.
Base circle: Base circle is the smallest circle, drawn tangential to the cam profile.
Trace point: Trace point is a point on the follower, trace point motion describes the movement of the follower.
Pitch curve: Pitch curve is the path generated by the trace point as the follower is rotated about a stationery cam.
Prime circle: Prime circle is the smallest circle that can be drawn so as to be tangential to the pitch curve, with its centre at the cam centre.
Pressure angle: The pressure angle is the angle between the direction of the follower movement and the normal to the pitch curve.
Pitch point: Pitch point corresponds to the point of maximum pressure angle.
Pitch circle: A circle drawn from the cam center and passes through the pitch point is called Pitch circle.
Stroke: The greatest distance or angle through which the follower moves or rotates.
CLASSIFICATION OF CAMS AND FOLLOWERS
CLASSIFICATION OF CAMS
Types of cam are as follow.
A. According to shape of cam
In this category, types of cam are classified by the shape of cam and profile of cam. These are as follows.
1. Radial or Disc cam
In radial cam, cam profile (shape of cam) is design in such way by which follower move as per the shape of cam or cam profile in perpendicular direction to the cam axis. There is always surface contact between cam profile and follower by spring force or gravity force.
2. Cylindrical cam
In cylindrical cam, follower axis and cam axis are parallel to each other. Cylindrical cam is cylindrical shaft on which profile made on cylindrical surface by machining. This profile is in the groove form and follower has surface contact with this groove. As cylindrical shaft or cylindrical cam is rotates follower move and movement of follower may be reciprocating or oscillating.
3. Translation or wedge cam
In this type of cam, cam is reciprocated and this movement is used to move follower. Cam has a specific shape or profile by which movement of follower is done.
4. Conjugate cam
In this type two discs are connected to each other and axes of discs are offset by the distance, to form cam profile. Follower has surface contact with cam profile by two rollers. As the cam rotate follower follow it.
5. Globoidal cam
Globoidal cam is shaft and has a concave or convex circumference. On which groove is made by machining and this groove is used for give movement to follower. Globoidal cam is used for oscillating follower about a fixed point.
6. Spherical cam
Spherical cam is in the form of spherical shape on which groove is made. Follower has surface contact with this groove. As cam rotate follower oscillate about a fixed point.
B. According to follower movement
In these category types of cam is classified as per movement of follower. Movement of follower is depending upon cam profile for this; cams are also classified according to follower movement.
1. Dwell Rise Dwell Return Dwell cam
In this type, follower movement is considering. As per name follower movement done in a way that first dwell then rise again dwell then return and again dwell. This all process is done in one rotation (360 degree) of cam.
2. Dwell Rise Return Dwell cam
In this type, follower movement is considering. As per name follower movement done in a way that first dwell then rise then return and again dwell. This all process is done in one rotation (360 degree) of cam.
3. Rise Return Rise cam
In this type, follower movement is considering. As per name follower movement is done in way that first rise then return. This all process is done in one rotation (360 degree) of cam.
4. Dwell Rise Dwell cam
In this type, follower movement is considering. As per name follower movement done in a way that first dwell then rise then again dwell. This all process is done in one rotation (360 degree) of cam. And at 360 degree it suddenly falls to its first position.
C. According to type of constraint of the follower
For proper function of cam and follower mechanism, it is important to keep surface contact between cam profile and follower at all time of rotation and any speed. For this need spring force, gravity force or positive drives are use in cam and follower mechanism. On this basis cams are classified by type of constraint of follower and these are as follow.
1. Preloaded spring cam
In this type of cam spring force is used. Compression spring is preloaded into follower in such a way that it maintains surface contact all time.
2. Positive drive cam
In this type of cam, it does not require any external force. The follower is design in such a way that it does not require any external force.
CLASSIFICATION OF FOLLOWERS
Types of followers are as follow.
A. According to surface in contact
Followers are classified by the surface contact between cam and follower is generally come in this group. There are different type of surface contact between cam and follower and according surface contact they are classified as follows.
1. Knife edge follower
As per name knife follower has knife edge and knife edge has a surface contact with cam profile (cam profile is a shape of cam). As follower has knife edge, so that there is more wear between follower and cam profile. Due to wear cam profile change with time and does not work correctly. That is reason due to which knife edge is not use in practice.
2. Roller follower
As per name roller follower has roller and surface contact between cam and follower is rolling contact. It reduces wear of cam profile.
3. Flat follower
Flat follower has flat profile at surface contact between cam and follower. It is useful where space is limited. Flat follower is used in automobile engine where space is limited.
4. Spherical follower
In flat face follower, stresses are produce. In order to reduce this stresses flat face is machined into spherical shape called as spherical follower.
B. According to type of follower motion
In this category followers are classified by the relative motion and movement between cam and follower these are as follow.
1. Translatory motion type follower
In this type of follower, follower have translatory motion means cam is rotating and follower reciprocating between guide way. Example of this type follower is knife edge follower, roller follower, flat follower and spherical follower.
2. Oscillatory motion type follower
In this type of follower, follower has oscillating motion. Cam rotates and as per cam profile follower also move but follower is fixed at point about which follower is oscillate. This type of follower is called as oscillatory motion type follower.
C. According to line of follower motion
In this category, followers are classified by the axis line of follower and these are as follows.
1. Radial follower
In radial follower, axis of follower and centre of cam are in one line or axis of follower is passing through centre of cam is called as radial follower. Example of this type follower is knife edge follower, roller follower, flat follower and spherical follower.
2. Offset follower
In offset follower, axis of follower movement is offset from the centre of cam about which cam rotate is known as offset follower.
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