07-08-2012, 04:36 PM
Kinematics &Dynamics of Machinery
Kinematics & Dynamics of machinery.pdf (Size: 2.26 MB / Downloads: 58)
Abstract
In kinematics and dynamics of machinery, were kinematics involves in finding out the
results of body in motion without considering the forces and dynamics involves in finding the
result of the body in motion with considering the forces. These analyses are carried out by
graphical, analytical and numerical method. The choice of approach to the solution is depend
on the problem at hand and the available data.
In general mechanisms are used to obtain various types of motion, one of the motion is
intermittent motion, to obtain the intermittent motion various type of mechanisms are used out
of which cam mechanism provides the best intermittent motion is been explained in the part-A
by comparing the advantage of cam over the other mechanism.
The wiper function is based on four bar mechanism were to obtain the crank rocker
motion synthesis of link length is carried out and modeled in ADAMS 2010 motion &
constrains are provided the result of displacement, velocity & acceleration is taken and the
effect of change in result by changing the crank length and coupler length is funded and the
results were compared and analysed.
Introduction & analysis of the statement:
Intermittent motion is the motion produced by mechanical device which starts and stops in a
regular interval. The major considerations involved in adapting these mechanisms are a) The
required indexing rate (number of steps per minute) b) Indexing accuracy required c) Dwell motion
pattern required d) The load to be operated ( heavy, medium or light duty) e) Cost consideration( an
expensive mechanism is acceptable or to be medium or low cost).
Comparison between Cam & Ratchet mechanism:
The reliability of ratchet mechanism is good as it engages in
tooth but not as good as cam mechanism and the ratchet mechanism
don’t offer any mechanical advantage in ratchet mechanism there is
presence of impact while the ratchet engagement which is not there in
cam. The indexing precision and the load carrying capacity are high
for cam than ratchet mechanism.
Comparison of Cam & Cycloid gear mechanism
The cycloid gear has very less load carrying capacity than cam. The
inputs to output the relative motion will be parallel in cycloid gear were as
both parallel and perpendicular motion is achieved in cam. The cost of
manufacturing of the cycloid gear is higher than cam. It has very less dwell
motion ratio and less indexing precision than cam.
Comparison between Cam & Geneva mechanism:
The Geneva mechanism can be operated at relatively low SPM
(strokes / minute) than cam mechanism. It can be used only for very slow
motions. The load carrying capacity and the control over the load is less
than cam mechanism.The indexing precision is less than cam mechanism.
Conclusion:
In the case study of diesel engine valve operation the cam is the only best option for
intermittent motion and though in different mechanical assembly various mechanisms are used to
obtain the intermittent motion other than cam but still cam has its own advantages and has wide
application in mechanical parts and there is no substitute for cam in some mechanism.