Page 23 - Dynamics of Mechanical Systems

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4 Dynamics of Mechanical Systems

• A joint is a connective member of a mechanism, usually bringing together two
elements of a mechanism. Two elements brought together by a joint are some-
times called kinematic pairs. Figure 1.4.1 shows a number of commonly used joints
(or kinematic pairs).
• A kinematic chain is a series of links that are either joined together or are in contact
with one another. A kinematic chain may contain one or more loops. A loop is
a chain whose ends are connected. An open chain (or “open tree”) contains no
loops, a simple chain contains one loop, and a complex chain involves more than
one loop or one loop with open branches.

Schematic Degrees
Joint Name Representation of Freedom
Revolute (pin) 1

Prismatic (slider) 1

Helix (screw) 1

Cylinder (sliding pin) 2

Spherical (ball and socket) 3

Planar 2

Universal (hook) 2

Spur gear (rollers) 1

Cam 1

FIGURE 1.4.1
Commonly used joints and kinematics pairs.