Low Cost Automation Tutorial

#060 Points on Single Axis Slide Mechanism Design

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December 3, 2010

For single axis slide based LCAs, pneumatic cylinders are often used for its ease of maintenance as shown in [Table 1] from the previous discussion. On the other hand, the easy to maintain characteristic seems to cause lack of completeness in preventative maintenance design concepts that should be considered in the first place.
Here, trouble examples of pneumatic actuator applications and countermeasure designs are explained.

(1) Pneumatic Actuator Troubles and Causes

Pneumatic actuator trouble causes and origins (where countermeasures should be addressed) are shown below.

Cause of Trouble	Origin
1. Mounting errors	Mechanism design
2. Inappropriate mounting position/direction	Mechanism design
3. Inappropriate actuator selection	Mechanism design
4. Inappropriate air supply quality	Maintenance activities
5. Inappropriate maintenance	Maintenance activities

(2) Trouble Examples and Countermeasures

The trouble details of 1.~3. above and countermeasures are explained below.

(1) Inappropriate Mounting to Mechanisms

Trouble Details

Explanations

Countermeasures

Connection Misalignments

Non-concentric relationship between the load center and cylinder piston drive center, causing misalignment strain on air cylinders. Reduced drive force, unstable velocity, and air leakages occur.

1.	Use of misalignment absorbing components (MISUMI Catalog: Floating Joints, etc.)
2.	Reevaluation of cylinder mounting methods (see [Table 1])
3.	Use larger diameter air cylinders

Excessive lateral loads on piston rods

Excessive lateral loads on piston rods causing air leaks from piston gaskets, rendering the cylinder unusable. (see [Fig.1])

1.	Design with no lateral loading
2.	Reevaluation of cylinder mounting methods
3.	Use of Long Rod/Long Bushing type to give lateral load immunity

Insufficient rigidity of mounting base

Insufficient rigid mounting base may suffer damages from shocks caused by load velocity dynamics

1.	Reinforced mounting base design (see [Fig.2])

Insufficient reliability and durability of air plumbing

Indiscriminate use of nylon tubes and quick couplings may cause problems over time. moving unit, heat effects, temperature variations, and chemical environments will require proper countermeasure

1.	Use screw-on couplings instead of quick couplings
2.	Use of Teflon tubes
3.	Proper tube lengths
4.	Securing the tubes and couplings

[Table 1] Mounting Methods of Pneumatic Cylinders (partly excerpted)

Travel Direction of Load	Cylinder Mount Method	Notes
Linear Motion Only	Foot Type Flange Type	Use when the load travel direction coincides with the cylinder axis center.
Linear Motion Only	Trunnion Type Clevis Type Eye Type Other	Use when the travel stroke is long or difficult to align load/cylinder axis centers.
When the load oscillates within one plane	Trunnion Type Clevis Type Eye Type	When the load oscillates within one plane, use clevises and trunnions movable directions in alignment with the oscillating direction. Also align the cylinder rod tip mounting joint oscillating direction.

[Fig.1] Internal Damages of Pneumatic Cylinder

[Fig.2] Pneumatic Cylinder Mount Reinforcement

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