Quick return mechanism 2 | Shaper Machine and Mechanical actuator Principle

Показать описание

Quick return mechanism | Shaper Machine and Mechanical actuator Principle
A quick return mechanism is an apparatus to produce a reciprocating motion in which the time taken for travel in the return stroke is less than in the forward stroke. It is driven by a circular motion source (typically a motor of some sort) and uses a system of links with three turning pairs and a sliding pair. A quick-return mechanism is a subclass of a slider-crank linkage, with an offset crank.

Quick return is a common feature of tools in which the action is performed in only one direction of the stroke, such as shapers and powered saws because it allows less time to be spent on returning the tool to its initial position.

History

During the early-nineteenth century, cutting methods involved hand tools and cranks, which were often lengthy in duration. Joseph Whitworth changed this by creating the quick return mechanism in the mid-1800s.[1] Using kinematics, he determined that the force and geometry of the rotating joint would affect the force and motion of the connected arm. From an engineering standpoint, the quick return mechanism impacted the technology of the Industrial Revolution by minimizing the duration of a full revolution, thus reducing the amount of time needed for a cut or press.
Applications
Quick return mechanisms are found throughout the engineering industry in different machines:

Shaper
Screw press
Power-driven saw
Mechanical actuator
revolver mechanisms
Design
The disc influences the force of the arm, which makes up the frame of reference of the quick return mechanism. The frame continues to an attached rod, which is connected to the circular disc. Powered by a motor, the disc rotates and the arm follows in the same direction (linear and left-to-right, typically) but at a different speed. When the disc nears a full revolution, the arm reaches its furthest position and returns to its initial position at a quicker rate, hence its name. Throughout the cut, the arm has a constant velocity. Upon returning to its initial position after reaching its maximum horizontal displacement, the arm reaches its highest velocity.

The quick return mechanism was modeled after the crank and slider (arm), and this is present in its appearance and function; however, the crank is usually hand powered and the arm has the same rate throughout an entire revolution, whereas the arm of a quick return mechanism returns at a faster rate. The "quick return" allows for the arm to function with less energy during the cut than the initial cycle of the disc.

Specifications
When using a machine that involves this mechanism, it is very important to not force the machine into reaching its maximum stress capacity; otherwise, the machine will break. The durability of the machine is related to the size of the arm and the velocity of the disc, where the arm might not be flexible enough to handle a certain speed. Creating a graphical layout for a quick return mechanism involves all inversions and motions, which is useful in determining the dimensions for a functioning mechanism.[2] A layout would specify the dimensions of the mechanism by highlighting each part and its interaction among the system. These interactions would include torque, force, velocity, and acceleration. By relating these concepts to their respective analyses (kinematics and dynamics), one can comprehend the effect each part has on another.
Dynamic Analysis
In addition to the kinematic analysis of a quick return mechanism, there is a dynamic analysis present. At certain lengths and attachments, the arm of the mechanism can be evaluated and then adjusted to certain preferences. For example, the differences in the forces acting upon the system at an instant can be represented by D'Alembert's principle.[6] Depending on the structural design of the quick return mechanism, the law of cosines can be used to determine the angles and displacements of the arm. The ratio between the working stroke (engine) and the return stroke can be simplified through the manipulation of these concepts.[7]

Despite similarities between quick return mechanisms, there are many different possibilities for the outline of all forces, speeds, lengths, motions, functions, and vectors in a mechanism.
In addition to the kinematic analysis of a quick return mechanism, there is a dynamic analysis present. At certain lengths and attachments, the arm of the mechanism can be evaluated and then adjusted to certain preferences.

Despite similarities between quick return mechanisms, there are many different possibilities for the outline of all forces, speeds, lengths, motions, functions, and vectors in a mechanism.