March 2011 Archives

Pneumatic actuators are the choice for LCA schemes in general for their ease of drive/control and low costs, instead of complex controls and performances. Here, some application examples of air cylinder LCA mechanism are introduced.
The examples shown are just references, and simply replicating them may not satisfy specific load requirements and expected positioning performances. Individual user application specific parameters and performance targets should be evaluated and appropriate designs should be applied with the guidelines shown below.

Air Cylinder Drive LCA Mechanism Design Reference Information

(1) Rack & Pinion, Link Mechanism LCA Examples (see [Fig.1])

(2) Soft Gripping Hand LCA Mechanism Example (see [Fig.2])

(3) Conveyor Diverter LCA Mechanism with Double Action Cylinders (see [Fig.3])

Diameter for factory wide air distribution plumbing is sized with increased future demands in anticipation. Additionally, the pipes accumulate scales and dusts on the internal walls from long term usage and the flow efficiency will be reduced. For these reasons, one size larger diameter than currently needed is generally selected.

When one size larger diameter is selected, the air flow increases by 3 times but the material cost increases only by 50%. Therefore, it is generally more beneficial to select tubes of larger diameter. The key to diameter sizing is to divide the system in two, "distribution" and "equipment connection" sections, and design to the following parameters.

	1.	Air volume to be handled
	2.	Max. air pressure used by air equipment
	3.	Plumbing length
	4.	Types and quantity of connection fittings in the system

"Distribution" and "Equipment Connection" designs are explained.

(a) Pipe Diameter Sizing for Distribution Section

	1.	Suppress terminal pressure drop to less than 0.5Kg/cm2
	2.	Size the pipe diameter based on the sum of air volume needed for all the equipment to be used.
	3.	Set the initial air pressure higher in the amount of pressure drop than the max. pressure needed for the highest rated air equipment.
	4.	Select connection fittings with consideration for air flow resistances (see [Table])
	5.	If pressure drop is a concern for long line lengths, provide an air tank in a intermediate location to prevent the pressure loss.

(b) Pipe Diameter Sizing for Equipment Connections

1.

Size pipe diameter based on max. air volume requirement of individual device connected.

(c) Cautionary Points on Equipment Connection Pipes (nylon & urethane tubes) and LCA

	1.	Make certain that used tubes do not have any external damages.
	2.	Cut off sections where damaged by repeated/prolonged usage.
	3.	Do not bend/fold tubes near connection fittings. (Min. bend radius for 6mm DIA. tube: 30mm, 8mm DIA. : 50mm)
	4.	When connecting to quick fitting threads, clean sealant off the internal threads of mating equipment.

Previous #072 and this #073 have been discussions on air system plumbing designs and usages.

On factory floors, compressed air is often perceived as free, therefore, compressed air plumbing design may be somewhat neglected. However, the quality of plumbing designs largely affects the air quality and air pressure losses, causing machine operation instabilities. Here, compressed air distribution plumbing designs will be explained in two parts.

(1) Distribution Plumbing Design

(1) Factory Floor Distribution Plumbing Basics

For general factory floor level plumbing, the Loop Method shown in [Fig.1] below is used.

Features of Loop Method Distribution Line

	1.	Able to supply uniform pressure air throughout the entire factory, even with small DIA. tubing.
	2.	The auxiliary tank assists in maintaining the maximum system pressure during momentary large air consumption periods, avoiding negative effects on surrounding air devices.

(2) Plumbing Methods of Main and Branch Lines

(a) Causes of Compressed Air System Plumbing Troubles

The air supplied from the compressor becomes likely to contain water condensation due to air expansion. The water condensation and lubrication oil from the compressor are mixed and the resultant emulsified fluid would flow in the distribution pipes with air. This emulsified fluid causes degradations of valves and air cylinders.

(b) Points on Plumbing Designs

The key is to design where the emulsions do not enter the branch lines from the main lines (see [Fig.2]).

Emulsion entering the air equipments can be prevented by following the below guidelines.

	1.	Provide main line incline in the direction of the air flow (Approx. 1cm per 1m incline)
	2.	Point the branching tees upward.
	3.	Mount water drain utilities on low points and end points.

(c) Points on Branch Line Connections to Air Equipment

The compressed air in the distribution plumbing contains rust, mold, and other impurities in addition to the emulsions. Air filters and lubricators should be installed to reduce friction variations and to prevent corrosions of air equipment slide components. Below are the points on air filter and lubricator connections.

	1.	Place air filters and lubricators within 5m.
	2.	Separately anchor the air equipment from the branch pipes to isolate unexpected air pressure related movements of branch lines.
	3.	For installations where distribution plumbing vibrations are expected, avoid use of solid steel or copper pipes and use flexible rubber and nylon tubes instead to prevent damages to air equipment.
	4.	Reduce the number of connections to improve system overall reliability.