Soctch yoke - dynamics lab experiments PDF

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DYNAMICS LAB Experiment No. 2 Scotch Yoke Mechanism Objective: To obtain the dynamics analysis in terms of velocity and acceleration of the slider crank and to study the working principle of scotch yoke mechanism

Apparatus:  Scotch yoke apparatus

 Meter rod  Degree meter showing crank position  Graph paper

Introduction: It is one of reciprocating motion mechanism, it should be convert an rotary motion into sliding of linear motion. When the Piston or reciprocating part to directly coupled together for the sliding of yoke including a slot. That engages a pin at reciprocating part. When the internal combustion engine to convert rotary motion into linear motion by means of crankshaft rotation. Where the Piston and connecting rod should be connected together. The Scotch Yoke Mechanism to be consider for more efficient because of the rotational motion to spent more time at high point of it rotate than Piston part.

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore.

DYNAMICS LAB Theory: The Scotch yoke (also known as slotted link mechanism[1]) is a reciprocating motion mechanism, converting the linear motion of a slider into rotational motion, or vice versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The location of the piston versus time is a sine wave of constant amplitude, and constant frequency given a constant rotational speed. Advantages of Scotch Yoke Mechanism  Easy construction of assembly and operation.  Used to perform of cutting, sliding and etc.  It is a directly convert method of rotary into Linear.  High torque to be made with small size of cylinder.  It spent high time in top dead center, so improve engine efficiency. Disadvantages of Scotch Yoke Mechanism  The high wear produced due to sliding friction and high contact pressure.  List percentage of time spent in bottom center position, to reduce the below time in two stroke engines.  The Piston motion is a pure sine wave will occur overtime give a constant rotation speed.  It requires proper guide way for reciprocating motion of arm.

Mechanism: 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, now the 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.

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore.

DYNAMICS LAB The crank is completed the clockwise Revolution at the same time the Yoke sliding completely moved in forward. When this position takes 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. By means of the full revolution of Crank, the Yoke will be sliding through equal of double length of Crank. The Yoke displacement can be controlled by varying of crank length.

Procedure: 1. Set the SCOTCH YOKE at 0mm for the connecting rod, and 0° for the rotating disk. 2. Measure R the radius for the rotating disk. 3. Change the angle for the disk by 30° each time until 360°, and each time measure X. 4. Fill the result in table (1). 5. Plot graphs between the angular displacement and the displacement X, velocity V, and the acceleration a.

Observations and Calculations: Sr. No.

Degree position

1 2 3 4 5 6 7 8 9 10 11 12 13

0 4.5 17 34 52 64.5 69 64.5 52 34.5 17 4 0

Displacement (mm) 0 0.45 1.5 2.8 4 4.8 5 4.7 3.9 2.7 1.4 0.35 0

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore.

DYNAMICS LAB

Graph:

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore.

DYNAMICS LAB

Slider crank mechanism vs scotch yoke mechanism: Basically slider crank is used to convert rotary motion to reciprocating motion and vice versa .It is a inversion of single slider chain which consist of a revolute pairs between connecting rod , crank and another revolute pair between connecting rod ,piston and a slider pair between engine cylinder and piston.In this mechanism cylinder (engine frame )is the fixed link.

Moving to the scotch yoke mechanism Similar to the slider crank chain it is also used to convert rotary motion to reciprocating motion and vice versa but in this mechanism two pistons are operated at a time as shown in below image.

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore.

DYNAMICS LAB

This is possible because two sliding pairs are there in this closed kinematic chain. In brief

Scotch yoke mechanism is a inversion of double slider crank chain which consist of two revolute pairs of link1 , link2 and link2 ,link 3.you can see that two sliding pairs (only one sliding pair in slider crank mechanism) of link 1 ,link3 and link 4(piston) ,link1.In this mechanism also link 1 is the fixed link.

Applications: This setup is most commonly used in control valve actuators in highpressure oil and gas pipelines. Although not a common metalworking machine nowadays, crude shapers can use Scotch yokes. Almost all those use a Whitworth linkage, which gives a slow speed forward cutting stroke and a faster return. It has been used in various internal combustion engines, such as the Bourke engine, SyTech engine,[2] and many hot air engines and steam engines. The term scotch yoke continues to be used when the slot in the yoke is shorter than the diameter of the circle made by the crank pin. For example, the side rods of a locomotive may have scotch yokes to permit vertical motion of intermediate driving axles.[3][4]

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore.

DYNAMICS LAB What is essentially a Scotch yoke, is used in the Tide-Predicting Machine No. 2 to generate a sinusoidal motion.

Comments: If we want precise and accurate process scotch yoke is best but due to two sliding pairs it has more friction as compared to the slider crank so in that respect it is costly and fuel inefficient.

Department of Mechatronics and Control Engineering University of Engineering and Technology, Lahore....