August 2010 Archives

　In order to plan a mechanism of high reliability and low cost, it helps to be able to imagine the concept as a simple and logical motion body.

Glossary of Basic Terms of Mechanisms

Terms Explanation Descriptive Symbols Mechanism Combination of multiple mechanical components where movement of a component results in movements of the others. 　 Driver and Driven Driver: The side with a prime mover. Input side. Solid Arrow Driven: The "moved" side. Output side. White Arrow = Explanation = A power transmission with two spur gears is a reversible system where the gears can rotate when Driver and Driven switch places. A worm and wheel gear combination is a non-reversible system where the worm can be the Driver side and function as a reducer transmission, but the inverse will not function. 　 Mechanical Element An element composing a mechanism 　 Pair A motion mechanism comprised of a pair (two) of mechanical elements. = Explanation = Categorized into two types depending on how the pair of machine elements contact. 　 Low Level Pair ： Surface Contact (sliding, rotating, screw) Sliding ： Shaft & Linear Bushing, Piston & Cylinder, etc. Rotation ： Pin & Metal Screw ： Bolt & Nut High Level Pai ： Point contact, Line contact pairing Point Contact ： Linear motion guides used ball bearing, etc. Line Contact ： Linear motion guides used roller bearing, etc. Sliding Pair

The lower level pairs are simple mechanisms and practical. The high level pairs are suitable for high speed and accuracy motion control, though knowledge on material selection and machining accuracy are required.

We have so far explained about air cylinders and linear motion guides as the representative machine elements for actuators and slide guides. Before proceeding on to explaining more wide variety of machine elements, concepts of mechanism will be explained.

(1) Differences between hand operations and mechanisms

Design and development concepts for assembly machinery (jig fixtures, semi-automatic machines, fully automatic machines) generally originated from hand operated assembling work. But it can be said that it is virtually impossible to perfectly replicate the movements of manual operations with mechanisms. It is not a good idea to attempt to imitate perception sensors, controls by brain, joints with multiple degrees of freedom, and handling with soft fingers of humans with mechanisms.
Mechanisms are suitable for the movements characterized by the following.

Therefore, the exact movements of hand operations are not to be replicated, though the concept is based on such, but the aim is to replace the hand operations with mechanical elements utilizing the characteristics 1~4.

(2) Fundamental Structure of Machinery (LCA)

Machines are the means to convert materials and parts (INPUT) into desired products (OUTPUT). The [Fig.1] is the fundamental structure. The Mechanisms apply assembling, machining, and moving operations to the (INPUT) and turn them into (OUTPUT).
The actuators (Drive Section) process the Energy, and the Information is processed by a controller (Control Section) to logically operate the mechanism.
All parts of machines are comprised of mechanisms but the most important mechanism is the section that creates the added value of (OUTPUT), and is called in a narrow sense the "Mechanism".