Table of Contents

Development of Multi Purpose Machine With Scotch Yoke Mechanism

INTRODUCTION

Multi-operation machine as a research area is motivated by questions that arise in industrial manufacturing, production planning, and computer control. Consider a large automotive garage with specialized shops. A car may require the following work, replace exhaust system, align wheels, and tune up. These three tasks may be carried out in any order. However, since the exhaust system, alignment, and tune-up shops are in different buildings, it is impossible to perform two tasks for a car simultaneously. When there are many cars requiring services at the three shops, it is desirable to construct a service schedule that takes the least amount of total time.

Scotch Yoke Mechanism

The Scotch yoke is a mechanism for 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 shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.

Read also :

Construction

The scotch yoke mechanism is constructed with iron bars. Here the crank is made in some length and the yoke is also made using the same material. It is noted that the minimum length of the 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.

Working principle

When the power is supplied to the 12v Dc motor, shaft and crank attached to the shaft start rotating. As the crank rotates the pin slides inside the yoke and also moves the yoke forward. When the crank rotates through in clockwise direction the yoke will get a displacement in the forward direction. The maximum displacement will be equal to the length of the crank. When the crank completes the next of rotation the yoke comes back to its initial position. For the next of rotation, yoke moves in the backward direction. When the crank completes a full rotation the yoke moves back to the initial position. For a complete rotation of crank the yoke moves through a length equal to double the length of the crank. The displacement of the yoke can be controlled by varying the length of the crank.

Advantages

High torque output with a small cylinder size
Fewer moving parts
Smoother operation
Higher percentage of the time spent at top dead center (dwell) improving theoretical engine efficiency of constant volume combustion cycles though actual gains have not been demonstrated.
In an engine application, elimination of joint typically served by a wrist pin, and near elimination of piston skirt and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is eliminated.

Disadvantages

Rapid wear of the slot in the yoke caused by sliding friction and high contact pressures.
Increased heat loss during combustion due to extended dwell at top dead center offsets any constant volume combustion improvements in real engines.
Lesser percentage of the time spent at bottom dead center reducing blow down time for two stroke engines, when compared with a conventional piston and crankshaft mechanism.

Applications

This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines
It has been used in various internal combustion engines, such as the Bourke engine, SyTech engine, and many hot air engines and steam engines.
It is also used in multipurpose machines and I.C engines.