To study and understand the functioning and application of crank and slotted lever quick return mechanism
Theory
Quick return mechanism is an inversion of a single-silder crank mechanism. The crank and slotted quick return mechanism converts rotatory motion into linear motion.
It is extensively used in shaping and cutting machines and is particularly useful in cutting flat surfaces out of metal stock. The return stroke of the ram is faster than the advancing stroke.
crank and slotted lever quick return mechanism
In the mechanism, as shown above the link AO corresponding to the connecting rod is fixed the solid disk rotates about center O and slotted lever AC due to constrain in it's motion oscillates about pivoted point A.A short link (connecting rod) CD transmits the motion from AO to the ram which carries the tool and reciprocates along the line of stroke.
Application of Quick return Mechanism
Shaper Machine:
The main application of the crank and slotted lever mechanism can be seen in Shaper Machine. To understand the crank and slotted mechanism let us elaborate the Shaper internal mechanism.
The shaper consists a tool that fixed to a Ram ; we can say that the ram is the part that will machine the workpiece. But the internal mechanism that allows the ram to move is the Crank and Slotted Lever Quick Return Mechanism. A gear is connected to the motor; the connecting rod and crank will turn in a way to achieve the sliding motion of the ram. In the quick return mechanism (whether crank and slotted or Whitworth), the backward movement of the ram is faster than the forward movement of the ram. Forward Movement is slower because the slow machining will give good finishing. The machining time of the crank and slotted lever mechanism can be taken as the ratio of time of cutting stroke (or forward stroke) to the time of return stroke (or backward stroke).
Video Simulation