DESIGN AND FABRICATION OF SLIDING RAM BY USING QUICK RETURN MECHANISM

Abstract:

This work aims to propose a novel design for quick return mechanisms, and the new mechanism is composed by a generalized Oldham coupling and a slider-crank mechanism. First, the kinematic dimensions that affect the time ratio are found by investigating the
geometry of the proposed design. By transforming into its kinematically equivalent mechanism, and then the design equations of time ratio are derived. Furthermore, a design example is given for illustration. Moreover, the design is validated by kinematic simulation using
ADAMS software. Finally, a prototype and an experimental setup are established, and the experiment is conducted. The results show that proposed new mechanism is feasible and with reasonable accuracy. In addition, it is more compact and easier to be balanced
dynamically than a conventional quick return linkage.
Quick-return (QR) mechanisms feature different input durations for their working and return strokes. The time ratio (TR) of a QR mechanism is the ratio of the change in input displacement during the working stroke to its change during the return stroke. Several basic types of mechanism have a QR action. These types include slider-crank and four-bar mechanisms. A project on QR mechanism design, within a first course on the theory of mechanisms, has been found to be effective for exposing students to concepts of mechanism design and analysis.
This paper reviews basic QR mechanisms, presents a project problem and solution examples, and discusses the value of inclusion of such project problems within theory-of-mechanism courses.

Introduction

A quick return mechanism is a mechanism that converts rotary motion into reciprocating motion at different rate for its two strokes. When the time required for the working stroke is greater than that of the return stroke, it is a quick return mechanism. It yields a significant
improvement in machining productivity. Currently, it is widely used in machine tools, for instance, shaping machines, power-driven saws, and other applications requiring a working stroke with intensive loading, and a return stroke with non-intensive loading. Several quick return mechanisms can be found in the literatures, including the offset crank-slider mechanism, the crank shaper mechanisms, the double crank mechanisms, and the Whitworth mechanism.

All of them are linkages. A linkage has its strengths and weaknesses. It is inexpensive to make and easy to lubricate; however, it is bulky and difficult to balance. In situations, if compact space is essential to the design, then a linkage may not be a good choice.
Therefore, how to find a new alternative of quick return mechanisms is an open topic that deserves to be examined. There are many scholars devoted to the studies of quick return mechanisms, and many valuable contributions have been made.