Kinematics of Machine Components Flashcards
It is a device that transforms one motion into another
Mechanism
Mechanisms which transmit
substantial forces, applying power, or
changing its direction.
Machine
When generated forces are associated
with the conversion of energy of high
temperature fluids to shaft power.
Engine
an assemblage
of rigid bodies coupled by mechanical
constraints such that there can be relative
motion between them
Mechanism
Two main constituents of Mechanics
Statics and Dynamics
Analysis of systems of rigid bodies
whose configuration is invariant with time
Statics
Analysis of systems of rigid
bodies whose relative configuration
changes with time.
Dynamics
The study of motion, without
considering the forces causing the motion:
position, orientation, displacement,
velocity, acceleration…
Kinematics
Equates motions to the forces that
cause them.
Kinetics
the distance
between every pair of points on the body is
constant during a motion)
Rigid body assumption
A process whose output prescribes
the sizes, shapes, materials and arrangements of components so that the resulting mechanism
will perform the desired task.
Synthesis
Techniques allowing for quantifiable evaluation of an existing, or proposed mechanism.
Analysis
indicates a joint between two
links
Kinematic pair
mechanical constraints imposed on the links.
Joints
Kinematic pair that involves surface contact
Lower pair
Those normally involving point, line, or curve contact
Higher pair
Kinematic pairs are classified based on
- Nature of contact
- Nature of mechanical constraint
- Nature of relative motion
Under classification of kinematic pairs according to nature of contact
Lower pairs
Higher pairs
Six types of lower pairs
Revolute or pin (R-Pair)
Prismatic pair (P-pair)
Helical pair (H-Pair)
Cylindrical (C-Pair)
Spherical (S-pair)
Planar pair (E-pair)
Lower pair that is made up of two congruent
mating surfaces of revolution. It has one rotational DOF
about its axis.
Revolute Pair (R-Pair)
Pair that is comprised of two congruent non-
circular cylinders, or prisms. It has one translational DOF
Prismatic pair (P-pair)
Also called screw. This pair is consists of two congruent helicoidally surfaces whose elements are a convex screw and a concave nut. 1 translational or rotational DOF, coupled by the pitch S
Helical pair (H-pair)
consists of mating convex
and concave circular cylinders. They can rotate relative to each other about their common axis, and translate
relative to each other in a direction parallel to the axis.
Hence the C-pair h
Cylindrical pair (C-Pair)
consists of a solid sphere which exactly conforms with a spherical shell. They are
also called ball-joints. They permit three rotational
DOF about intersecting orthogonal axes.
Spherical S-pair
German word for plane
Ebene
special S-pair comprising two
concentric spheres of infinite radius. They permit two orthogonal translations and one rotational DOF about
an axis orthogonal to the plane of translation. They
provide three DOF in total.
Planar (E-pair)
If two links have a sliding motion relative
to each other, they form a
Sliding pair
When one link has a turning or
revolving motion relative to the other, they constitute
Turning pair
When the links of a pair have a rolling
motion relative to each other, they constitute a
Rolling pair
If two mating links have a turning as well
as sliding motion between them, they form a
Screw pair
When one link in the form of a sphere
turns inside a fixed link, it is a
Spherical pair
The relative motion is pure
translation as in a reciprocating cam
activating a knife-edge or mushroom head
follower, or the finger tip of a robot hand
sliding on a at surface.
Pure sliding
The relative motion involves
rolling without slip, such as the tangential
pitch circles or mating sets of spur gears, or
rack and pinion system
Pure rolling
A body which is if under
the action of forces, it does not suffer any
distortion.
Rigid body
Those which are rigid for the purpose they have to serve
Resistant bodies
Which are normally flexible,
but under certain loading conditions act as
rigid body for the limited purpose.
Semi-rigid body
Kinematic Pairs according to Relative Motion
Sliding Pair
Turning pair
Rolling pair
Screw pair
Spherical pair
Pure sliding
Pure Rolling
Combination of Sliding and Rolling
When the elements of a pair are
held together mechanically, they are
Closed pair
When two links of a pair
are in contact either due to force of gravity
or some spring action,
Unclosed pair
defined as the number
of independent relative motions both translational and rotational.
Degrees of freedom
A resistant body or a group of resistant
bodies with rigid connections preventing their relative movement is known as
Link
an assembly of links in
which the relative motions of the links is
possible and the motion of each relative to
the other is definite.
Kinematic chain
does
not allow any motion of a link relative to the
other.
Redundant chain
If motion of any of the movable links
results in definite motions of the others the
linkage is known as
Mechanism
If one of the links of a redundant chain is fixed, it is known as
Structure
