Classification of Cams and Followers
There is not a general classification for cam mechanical systems. However, the 'functional embodiments' and 'functions' of each sub-system have relatively few possibilities, which we can classify.
Note:
There is often confusion with the term cam-follower, in English at least. The term Cam-follower is often used for both the element that is in direct contact with the cam and the element that has its motion defined by the cam.
Where possible, I will use the term Cam-Follower for the part that has its motion defined by the cam.
There are two common shapes of the element that are in direct contact with he Cam - circular and flat. I will use the term Cam-Roller Follower when it is rolling bearing, and Flat-Faced Follower when it is a Flat-Face. For other shapes, it should be clear. from the context.
A General Classification of Cam and Cam-Follower Types:
The general shape of the cam is generated by the interaction of the cam and follower motions.
Planar:
| • | The cam is a disc, plate, track, groove, conjugate, ramp, slot |
Spatial:
| • | Spatial: the cam is cylindrical, barrel, globoidal, |
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The modes of cam motion are:
Rotating Cams:
| • | The cam swings back and forth: ; the cam 'oscillates' |
| • | The cam rotates continuously |
Translating Cams:
| • | The slide back and forth; the cam 'reciprocates' |
Stationary Cams:
| • | The cam is a plate that is nominally 'Circular', fixed to a frame (most common on rotating machinery - such as bottle labelling, capping and filling machines). |
| • | The cam is a ramp that is nominally 'Linear', for example it is a 'slot' or 'ramp'. |
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The shape of the follower influences the shape of the cam.
| • | Cylindrical Roller Follower |
| • | Taper Roller Follower - use with barrel, globoidal and other non-planar cams. |
| • | Barrel (also called a Crowned) Roller Follower. |
| • | Logarithmic Roller Follower - the actual function is the intellectual property of each manufacturer. |
| • | Knife-edged Follower - not a practical cam-profile shape, but included here for completeness |
See Typical Cam-Profile Shapes
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The modes of cam-follower motion are:
Rotating Followers: a lever:
| • | Swing back and forth: an oscillating follower |
| • | Progressive motion, they index, in one direction |
Translating Followers: a slider:
| • | Sliding back and forth: a reciprocating follower |
Stationary Followers:
| • | The Stationary Cam-Follower moves the Cam, not as common, molding machines, wedge |
| • | A stationary follower might be used to position a cam part, like a 'wedge' cam. |
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The constraint between the cam and the follower shape influences whether the cam is 'open' or 'closed'.
Force Closed:
The constraint between cam-follower and the cam is with:
| • | Gravity, Spring, Air-Cylinder, ... |
Form Closed (also called Body Closed):
The constraint between the cam-follower and the cam is with a:
| • | Groove (Track), Rib, Slot, within which the cam-follower is constrained. |
| • | Conjugate Cams: these systems require manufacturing and production accuracy for a follower to be in contact with each cam. |
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Non-progressive:
The follower returns to the same position after each cycle by reversing its direction of motion at some point in the cycle.
Progressive: (also called 'indexing', see also Indexing Cams) )
The follower moves progressively to a new position at the end of each cycle.
In most cases the follower is replaced by another follower at the end of a motion cycle. Equally spaced followers return to their original positions after a number of motion-cycle. Most indexing systems use several roller followers equally spaced around a follower wheel or 'turret'.
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Cam Motion