The objective of this experiment is to investigate the kinematics motion of a Crank and Slotted Lever Quick Return mechanism. The investigation is to show that it is indeed a quick return mechanism and to evaluate the increase in efficiency that this would offer if applied to a machine tool.
Definition of a Mechanism
A mechanism is a simplified model, usually in the form of a line diagram, which is used to reproduce the motion occurring in a machine. The purpose of this reproduction is to enable the nature of the machine. The purpose of this reproduction is to enable the nature of the motion to be investigated without the encumbrance of the various solid bodies which form the machine elements The various parts of the mechanism are called links or elements. Where two links are in
contact and a relative motion is possible, then they are known as a pair. An arbitrary set of a links which form a closed chain that is capable of relative motion, and that can be made into a rigid structure by the addition of a single link, is known as a kinematics chain. To form a mechanism from a kinematics chain one of the links must be fixed. However as any of the links can be fixed, it follows that there are as many mechanism as there are links in the chain. The technique obtaining different mechanism by fixing the various links in turn is known as inversion.
The relative motion between two links of a pair can take different form. Three types of a pairs are known as lower pairs and these are the frequently occurring ones:Sliding : such as occurs between a piston and a cylinder Turning : such as occurs with a wheel on an axle Screw motion : such as occurs between a nut and a bolt All other cases are considered to be combinations of sliding and rolling are called higher pairs. Strictly screw motion is a higher pair as it combines turning and sliding. Slider – Crank Mechanism The slider- crank mechanism is well known as the basis of a reciprocating engine. As shown in the diagram below it consists of three turning pairs and one sliding pair
|Fig. slider- crank mechanism|
In the above diagram, the link 1 is fixed. If we now fix link 2, that is consider an
inversion of the mechanism, we obtain the mechanism shown below. This is known as Whitworth Quick Return Mechanism.
|Fig. Air Compressor Using Crank and Slotted Link Mechanism|