10-12-2012, 05:19 PM
MYSORE Slider Crank Mechanism
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Slider Crank Mechanism
Slider-Crank Mechanism, arrangement of mechanical parts designed to convert straight-line motion to rotary motion, as in a reciprocating piston engine, or to convert rotary motion to straight-line motion, as in a reciprocating piston pump. The basic nature of the mechanism and the relative motion of the parts can best be described with the aid of the accompanying, in which the moving parts are lightly shaded. The darkly shaded part 1, the fixed frame or block of the pump or engine, contains a cylinder, depicted in cross section by its walls DE and FG, in which the piston, part 4, slides back and forth.
Principal Parts Of Slider-Crank Mechanism.
The conventional internal combustion engine employs a piston arrangement in which the piston becomes the slider of the slider-crank mechanism. Radial engines for aircraft employ a single master connecting rod to reduce the length of the crankshaft. The master rod, which is connected to the wrist pin in a piston, is part of a conventional slider-crank mechanism. The other pistons are joined by their connecting rods to pins on the master connecting rod. To convert rotary motion into reciprocating motion, the slider crank is part of a wide range of machines, typically pumps and compressors. Another use of the slider crank is in toggle mechanisms, also called knuckle joints. The driving force is applied at the crankpin so that, at TDC, a much larger force is developed at the slider. See also Four-bar linkage.
The crank has a mass m1 (and length L1), while the connecting rod has a mass m2 (and length L2). Gravity in the -Y direction is included, as is the force F acting on the piston. The equations will be generated in the 3 joint coordinates [?, ß, s]. Since the system has only 1 degree of freedom, 2 algebraic constraint equations will be generated for these 3 coordinates, in addition to the 3 dynamic equations. Slider-Crank Mechanism changes the rotary motion of the power source (Electric motor) into the reciprocating motion of the ram.
WHITWORTH SLIDER-CRANK MECHANISM
Whitworth quick return mechanism is shown in figure. Crank BC revolves at a uniform speed. During cutting stroke the point ‘C travels from Y to X through Z. The ram is returned at high speed as the crank rotates from X to Y though ‘T’
Crank Mechanism
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod. The end of the rod attached to the crank moves in a circular motion, while the other end is usually constrained to move in a linear sliding motion, in and out.
The term often refers to a human-powered crank which is used to manually turn an axle, as in a bicycle crank set or a brace and bit drill. In this case a person's arm or leg serves as the connecting rod, applying reciprocating force to the crank. Often there is a bar perpendicular to the other end of the arm, often with a freely rotatable handle on it to hold in the hand, or in the case of operation by a foot (usually with a second arm for the other foot), with a freely rotatable pedal.
Crank Mechanism such as the one seen opposite is used where there is a need to convert rotary motion into reciprocating motion. Many machines have this type of mechanism and in the school workshop the best example is the shaping machine.