Quick Return Mechanisms

 

QUICK RETURN MECHANISM

GROUP C-4 MEMBERS : 

Pranav Nagane (16), Ganesh Naik (17), Manish Naik (18), Muthu Krishnan(19), Neil Yardi (20), Varad Nikam (21)

Guide: Prof. Umesh Chavan 

What is a Quick return mechanism?

A quick return mechanism is an apparatus that consists of a system of links with 3 turning pairs and a sliding pair that can convert rotary motion into reciprocating motion. The time taken for travel in return stroke is less than in forwarding stroke.

• A quick return mechanism is also known as a Crank and slotted lever quick return motion mechanism.
• It consists of 3 turning pairs and one sliding pair as shown below.

3 Types of Quick Return Mechanism | Effortless Mechanism in Shaper Machine

There are three types of the quick return mechanism

1. Hydraulic drive

2. Crank and slotted link mechanism

3. Whitworth mechanism

A quick return mechanism is a mechanism that produces a reciprocal effect so that the system takes less time in the return stroke while comparing with forwarding stroke. In the quick-return mechanism, a circular movement like the crank and lever mechanism is converted into reciprocal movement but the return time is different from the forward moment. In several applications, this process is used. Some of them are shaper, slotter, screw-press, mechanical drive, etc. The time required for cutting is reduced with the assistance of a quick return mechanism.

HYDRAULIC DRIVE

       Inside the hydraulic cylinder, a piston reciprocates. Between the piston and the ram, a piston rod is connected. So, the ram reciprocates along with the piston. Two entries are provided near each end of the cylinders. A four-way control valve connects these two entries with the reservoir which contains the fluid. The reservoir is connected to the valve with the help of drain pipes and a supply pipe.

Hydraulic Mechanism – Quick Return Mechanism

 

      The supply pipe is again connected to the reservoir by a pump and relief valve. The valve is actuated by the lever and trip dog fitted to the ram. Oil is sucked by the gear pump from the reservoir at a particular pressure. This high-pressure oil goes to the cylinder through the four-way valve.

       The oil is allowed from the pump to the left side of the piston forces the piston to move the ram towards the right (R). It is called a forward or cutting stroke. In this stroke, oil flows out on the right side entry to the reservoir through the four-way valve and drain pipe. The lever hits one trig dog at the end of this stroke.

       Now, the lever position is changed. Due to this, the supply pipe supplies the oil on the right side of the piston which moves the ram towards the left called a return stroke or nan-cutting stroke. in this stroke, the high-pressure oil covers the lesser area on the cylinder. Due to this, the pressure force will increase. Hence, this return stroke is faster by supplying the same quantity of oil.

CRANK AND SLOTTED LEVER MECHANISM

          In this mechanism, the ram is actuated by gear drives associated with an electric motor. First, the electric motor drives the pinion gear. Next, the pinion gear drives the bull gear which rotates in opposite direction due to external gear meshing. A radial slide is provided on the bull gear. A sliding block is assembled on this slide. The block can be positioned in the radial direction by rotating the stroke adjustment screw.

Crank And Slotted Lever Mechanism – Quick Return Mechanism

 

          The sliding block has a crank pin. A rocker arm is freely fitted to this crank pin. The rocker arm sliding block slides in the slot provided in the rocker arm called a slotted link . The upper end has a fork that is connected to the ram block by a pin while the bottom end of the rocker arm is pivoted.

Schematic Arrangement Of Crank And Slotted Lever Mechanism – Quick Return Mechanism

 

         When the pinion gear rotates along with the bull gear, the crank will also rotate. Due to this, the rocker arm sliding block also rotates in the same circle. Simultaneously, the sliding block slides up and down in the slot. This movement is transmitted to the ram which reciprocates. Hence, the rotary motion is converted into reciprocating motion.

WHITWORTH QUICK RETURN MECHANISM

         The shaft of an electric motar drives the pinion which rotates the bull gear. The bull gear has a crank pinion. A sliding block slides over this crankpin and slides inside the slot of a crank plate. A connecting rod connects the pin at one end and the ram at the other end.

Whitworth Quick Return Mechanism

 

 LASER Beam Welding | LASER Cutting System

        When the pinion rotates, the bull gear is also rotated along with the crank pin. At the same time, the sliding block slides on the slot provided on the crank plate. This makes the ram move up and down by the connecting rod.

The two important cases in this mechanism are

1. At an angle of the bull gear rotates in an anticlockwise direction and the ram moves in a forwarding direction.

2. When the bull gear rotates further in the same direction at an angle of the return stroke will take place. Here the angle is lesser than the angle. So, the time taken for the return stroke is reduced.

Applications of Quick Return Mechanism:

These are the following applications of the Quick return mechanism:

1. It is used in the shaper Machine for flattening the workpiece.
2. The same is used in the Slotter and Planer Machine.
3. It is also used in the Screw press, Mechanical actuator, and Rotary combustion Internal Engine.

Advantages of Quick Return Mechanism:

These are the advantages of the Quick return mechanism:

1. The process is automated.
2. The construction of the mechanism is not so complicated.
3. It can perform operations like cutting, flattening, and slotting the workpiece.
4. The idle time is reduced because of the fast returning stroke.

Disadvantages of Quick Return Mechanism:

Disadvantages of the Quick return mechanism are:

1. In the returning stroke, there is no contact with the work so no cutting takes place hence the process takes much time to complete.
2. The forward stroke takes much time compared to the return stroke.
3. It takes more power to perform operations.
4. There is friction in the slider and Piston.
5. Continuous it won’t work because of heat generated inside the piston and wear and tear can happen.
6. Balancing of linkage is also a major problem as this device is also linked to linkages.

Conclusion:

So there you have it, an in-depth article on Quick-Return Mechanism.

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References

Books:

1. A. K. Mallik, A. Ghosh, and G. Dittrich - Kinematic Analysis and Synthesis of Mechanisms, CRC Press Inc. Boca Rato
2. A. Ghosh and A. K. Mallik - Theory of Mechanisms and Machines, Affiliated East-West Press (P) Ltd., New Delhi
3. Phakatkar H. G. (1999) Theory of Machines and Mechanisms-I, Nirali Prakashan.
4. Robert J. Schilling (2003) Fundamentals of Robotics: Analysis and Control. Prentice-Hall Inc.
5. Ghosal A (2006) Robotics: Fundamental Concepts and Analysis, Oxford University Press.

Papers NPTL

1. https://nptel.ac.in/courses/112/104/112104121/