SCOTCH YOKE MECHANISM

 SCOTCH YOKE MECHANISM 

• INTRODUCTION:

The scotch yoke mechanism is a simple mechanism for changing the linear motion of a slider into rotary motion or vice versa. The parts of this device include a sliding bar, a yoke on the bar with a slot cut out, and a smaller bar connected to the yoke and fixed by a pin through the yoke slot to the slippery bar.

The scotch yoke mechanism is used to convert the rotary motion of the crank into sliding motion. As the crank rotates, the horizontal portion of the link slides or reciprocates in the fixed link. Scotch yoke mechanism is obtained when one of the sliding links of a double slider crank chain is fixed.

fig. scotch yoke mechanism

The advantage of scotch yoke mechanism over the slider crank mechanism is that it has lesser moving parts and smoother operation. This mechanism is most commonly used in control valve actuators in high pressure oil gas pipelines. It is also used in various internal combustion engines.

 As the bar slides back and forth, or reciprocates, the smaller bar is forced to slip up and down within the yoke slot, making a motion movement. In operation, the reciprocating part is directly coupled to the sliding bar or yoke with a slot that engages the pin on the rotating part. 

The motion of the Scotch Yoke Mechanism is such that pure simple harmonic motion is produced by the mechanism when driven by an crank. Scotch Yoke Mechanism is most ordinarily utilized in management valve actuators in high oil and gas pipelines. Although not a common metal working machine nowadays, crude shapers also use Scotch yokes.

• CONSTRUCTION :

The scotch yoke mechanism is constructed with iron bars. Here the crank is made in some length say (10 cms ) and the yoke is also made using the same material. Also the minimum length of yoke should be double the length of the crank.

 The crank and yoke is connected with a pin. Iron bars are welded to both sides of the yoke to get the reciprocating motion. The yoke with the iron bars is fixed on the display board with the help of c clamp. 

Now the crank is welded to the end of the shaft of the motor. Now the pin on the crank is connected to the yoke. The pin used to connect yoke and crank is a bolt. The whole setup displayed in a plywood board.

• WORKING :

It is a simple mechanism, the rotary motion of pin convert into linear motion. First, the power supplied to be connected in DC motor, when the shaft to start in rotation moment then crank rotate the pin slider inside of yoke part and also move in forward direction. 

When the Crank will be rotate in clockwise direction and yoke will be getting displacement moment at forward. The maximum displacement of yoke depends upon the length of Crank.

The crank is completed the clockwise Revolution at the same time the Yoke sliding completely moved in forward. When this position take more time to start return stork. After spent time, the crank will be rotate in continuously it to be come back in initial position of rotation.

 So the Yoke move in backward direction and come back for initial position. Therefore the crank has full Revolution to be completed. At the same time the Yoke will be complete the forward and backward movement of Sliding.  The full revolution of Crank, the Yoke will be sliding through equal of double length of Crank. The Yoke displacement can be controlled by changing crank length.

• APPLICATIONS:

1. DESIGN AND FABRICATION OF WATER PUMP USING SCOTCH YOKE MECHANISM :

fig. Design and fabrication of water pump using scotch yoke mechanism

The setup consists of water pump whose pumping shaft is connected to the yoke plate of the scotch yoke mechanism the rotating disk consists of the yoke supporting pin is inserted into the yoke plate for controlling the translation motion.

The rotation of the plate is carried out with the help of motor. When the motor is turned on then it rotates the plate attached with it and this rotation is converted into translation by means of yoke plate, this translation motion activates the piston of the pump to take to and fro motion, the water is sucked and transmitted to the required place.

2. DOUBLE ACTING HACKSAW USING SCOTCH YOKE MECHANISM

Double acting power hacksaw cuts two material simultenously by its scotch yoke mechanism , so the production rate increases twice than that of power hacksaw.

 Double acting power hacksaw works under by the scotch yoke mechanism. The scotch yoke mechanism converts the rotary motion into reciprocating motion.

• ADVANTAGES :

1. Easy construction of assembly and operation.
2. Used to perform cutting, sliding etc.
3.  It is a directly convert method of rotary into Linear.
4. High torque to be made with small size of cylinder.
5.  It spent high time in top dead center, so improve engine efficiency.

• DISADVANTAGES :

1.  List percentage of time spent in bottom center position, to reduce the below time in two stroke engine.
2.  The Piston motion is a pure sine wave will occur overtime give a constant rotation speed.
3.  It requires proper guide way for reciprocating motion of arm.
4. The high wear produced due to sliding friction and high contact pressure.

CONTRIBUTERS:

1. DIPAK KHATALE

2. KAUSTUBH BORSE

3. ROHAN KHEKADE

4. SHARAYU KHANDAGALE

5. YUKTA KHAIRNAR