CHAPTER 5: Cams: Design
and Kinematic Analysis
5 .1 Introduction
5.2 Types of cam and follower
5.3 Follower motion scheme
5.4 Pressure Angle
5.5 Cam Profile Design
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5.1. Introduction
Cam is a common
mechanism element
that drives a mating
component known as
a follower
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5.2. Types of cam and follower
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5.2. Types of cam and follower
Pivoted
follower
Translating
follower
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5.2. Types of cam and follower
Pivoted
follower
Translating
follower
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5.2. Types of cam and follower
Follower shape:
knife-edge follower
roller follower
flat-faced follower
spherical-faced follower
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5.3. Follower motion scheme
PRESCRIBED FOLLOWER MOTION
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5.3. Follower motion scheme
A cam is to be used for a platform that will repeatedly lift boxes from a lower
conveyor to an upper conveyor. Plot a displacement diagram and determine the
required speed of the cam when the follower motion sequence is as follows:
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=15.38 rpm
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5.3. Follower motion scheme
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5.3. Follower motion scheme
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5.3. Follower motion scheme
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5.3. Follower motion scheme
Constant Velocity Motion
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5.3. Follower motion scheme
Constant Velocity Motion
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5.3. Follower motion scheme
Cycloidal motion
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5.3. Follower motion scheme
Cycloidal motion
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5.3. Follower motion scheme
Cycloidal motion
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5.3. Follower motion scheme
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5.3. Follower motion scheme
Constant Acceleration Motion
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5.3. Follower motion scheme
Constant Acceleration Motion
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5.3. Follower motion scheme
Constant Acceleration Motion
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5.3. Follower motion scheme
Constant Acceleration Motion
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5.3. Follower motion scheme
Harmonic Motion
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5.3. Follower motion scheme
Harmonic Motion
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5.3. Follower motion scheme
Harmonic Motion
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5.3. Follower motion scheme
Harmonic Motion
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5.3. Follower motion scheme
EXAMPLE A cam is to be designed for an automated part loader. Using the
motion equations, construct a chart that tabulates follower
displacement versus time and cam rotation. Also plot this data
when the prescribed motion for this application is as follows:
4.25s
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5.3. Follower motion scheme
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5.3. Follower motion scheme
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5.3. Follower motion scheme
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5.3. Follower motion scheme
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5.4. Pressure Angle
Because a force is always transmitted
perpendicular to surfaces in contact,
the cam does not always push the
follower in the direction of its motion.
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5.4. Pressure Angle
The force required to push the follower depends on the
application of the cam system.
However, the contact force between the cam and follower can be
much greater, depending on the location of the contact point.
Actually, only one component of the contact force generates the
follower motion.
The other force component is undesirable as it generates a side
load and must be absorbed by the follower guide bearings.
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5.4. Pressure Angle
The pressure angle, δ, correlates
these two components of the
contact force.
The pressure angle, at any point on
the profile of a cam, is the angle
between the follower movement
and direction that the cam is
pushing it.More precisely, it is the
angle between the path of the
follower motion and the line
perpendicular to the cam profile at
the point of follower contact.
Each point on the cam surface has
a pressure angle.
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5.5. Cam Profile Design
The base circle is the smallest circle centered on the cam rotation axis
and tangent to the cam surface.
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5.5. Cam Profile Design
The trace point serves as a reference to determine the effective location of
the follower.
For a knife-edge follower, it is the point of cam and follower contact.
For a roller follower, the trace point is chosen at the center of the roller.
For a flat- or spherical-face follower, the trace point is chosen on the
contact surface of the follower.
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5.5. Cam Profile Design
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5.5. Cam Profile Design
For ease in cam profile construction, kinematic
inversion will be used. The cam will be imagined
as being stationary. The follower then should be
rotated opposite to the direction of cam rotation.
The desired location for the follower, at several
positions, is constructed from the base circle.
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5.5. Cam Profile Design
Graphical Disk Cam Profile Design
In-Line Knife-Edge Follower:
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5.5. Cam Profile Design
Graphical Disk Cam Profile Design
In-Line Knife-Edge Follower:
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5.5. Cam Profile Design
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5.5. Cam Profile Design
Graphical Disk Cam
Profile Design
In-Line Roller Follower:
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
ANALYTICAL DISK CAM PROFILE
DESIGN
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5.5. Cam Profile Design
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5.5. Cam Profile Design
Example:
Analytically determine the cam profile
coordinates when a knife-edge follower is
incorporated. Because of the size
constraints of the machine, a cam with a
base circle diameter of 200 mm must be
used. The cam is to rotate
counterclockwise.
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
Example: Two cams are used to drive a gripper of a mechanical part handler.
The two cams can generate independent horizontal and vertical motions to the
gripper. Such machines can relocate parts in a similar fashion to a robot at a
fraction of the cost. The part handler is shown in Figure below
The prescribed motion for one of the cam followers is as follows:
1. Rise 1.5 in. in 1.5 s using the harmonic motion scheme.
2. Dwell for 2 s.
3. Return in 1.5 s using the harmonic motion scheme.
4. Dwell for 2 s.
5. Repeat the sequence.
An in-line roller follower with a radius of 0.5 in. is used on a cam with a
base circle radius of 3.5 in.
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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5.5. Cam Profile Design
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