of one of the simple motions, such as rotation, into any other
motions is often conveniently accomplished by means of a cam
mechanism. A cam mechanism usually consists of two moving
elements, the cam and the follower, mounted on a fixed frame.
Cam devices are versatile, and almost any arbitrarily-specified
motion can be obtained. In some instances, they offer the
simplest and most compact way to transform motions.
cam may be defined as a machine element having a curved outline
or a curved groove, which, by its oscillation or rotation
motion, gives a predetermined specified motion to another
element called the follower. The cam has a very important
function in the operation of many classes of machines, especially
those of the automatic type, such as printing presses, shoe
machinery, textile machinery, gear-cutting machines, and screw
machines. In any class of machinery in which automatic control
and accurate timing are paramount, the cam is an indispensable
part of mechanism.
cam is a specially shaped component that serves to guide the
motion of a component called a follower. The cam has a rotary
or linear motion. The most important advantage of cam principle
is that it is quite conveniently possible to introduce pauses
of any desired length into the motion. This advantage is widely
used in machinery of all kinds, such as packaging machines
and many others. Using cams it is possible to perform simple
sliding movements or oscillatory. It can also precisely controlled
movements of elaborate shape.
e.g, Guiding a milling cutter along a curved outline of any
desired shape. A cam mechanism (Figs.1.2 & 3) basically
consist three parts: the frame or base (a), on which the cam
(b) is mounted, and the follower (c) whose motion is controlled
by the cam, which is given a linear (Fig.1) or a rotary (Figs.2
and 3) motion. A follower is a component which is specially
shaped component of cam used to guide its motion.
suitable example of a cam mechanism is the valve gear of an
internal-combustion engine (Fig.4). The rotating cam has an
approximately pear-shaped profile comprising two circular
curves joined by two straight lines which are tangential to
those curves. The follower consists of a roller tappet which
is moved up and down by the cam and imparts this motion to
the rod that controls the opening and closing of the valve.
The center of the roller traces a curve of similar shape to
the cam profile.
Fig.5 the stroke, the speed and the acceleration of the roller
tappet have been plotted against the angle of rotation the
acceleration undergoes a sudden change in value, which imparts
a jerk to the tappet. This occurs every time the radius of
curvature of the cam profile changes abruptly e.g., transition
from circular curve to tangent and vice versa. Conversely,
it is possible to start from a certain acceleration curve
that comprises no abrupt changes (red curve in Fig.5) and
design a cam so shaped as to gentle acceleration, free of
shows a cam mechanism whose two paths can so move a milling
cutter in two mutually perpendicular directions that a cut
conforming to a specific shape (in this case the letters HB)
can be produced. The two cam paths are determined as follows:
The trace is subdivided into a number of approximately equal
portions (22 in the present example).
the distances that the cutter has to move in the horizontal
and vertical directions, respectively, to reach this point
from the initial position 0, are plotted in two diagrams for
all the points (0 to 22). Then the circumference of the cam
disc is also divided into 22 equal parts. From 19 to 22 the
cutter must moreover be lifted off the work, since this constitutes
the return motion to the starting point.
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