Low Cost Automation Tutorial: May 2012 Archives

May 2012 Archives

#116 High Rigidity Disc Couplings

By システム管理者 on May 25, 2012 12:00 AM | No Comments | No TrackBacks

(1) What is a coupling?

One of the machine elements connecting a motor to a rotating drive mechanism is a coupling. Demands for high accuracy, rigidity, speeds on rotating power transmission mechanisms are on the increase as advanced digital controls are implemented.

(2) Role of the couplings

When connecting a rotating motor and a shaft (ball screw, etc.) even accurately, varying conditions occur in motion.

(1) Deflections of rotating shafts (ball screws, etc.)
(2) Deflections and deflection stress of two shafts caused by heat expansion
(3) Deformation of ball screw support section
(4) Deviation of bearing wear friction after long usage durations

In order to resolve the variable elements (1) ~ (4) above, couplings (deflecting shaft connectors) are used.

(3) Functionalities required for couplings

a) High rigidity --- To cope with high accuracy and high speeds of servo systems

Explanation
If the coupling rigidity is insufficient, servo system delays (lost motion) occurs and positioning accuracy would be degraded, and causes resonance.

b)Zero backlash --- To cope with high accuracy of servo systems

Explanation
Zero backlash couplings without any sliding elements should be selected since mechanical backlash (clearance) is detrimental for servo systems. For the method of shaft mounting, friction fixed mounting is preferred over key fixed mounting.

c) Low inertia --- To improve servo system response

d) Damping characteristics --- To suppress drive system resonances

New products: Characteristics of high rigidity disc couplings

	*	Product compatible to servo motors with excellent high speed and accurate controllability.
	*	Due to their disc configuration, they have virtually zero backlash, but have high flexibility in shaft misalignments such as angular and shaft center misalignments. Easy to accomplish shaft aligning work.
	*	The clamp style mounting eliminates a need to machine the shaft for keys. No concerns for shaft strength degradation.

New product: High rigidity disc style couplings

#115 Clean Room Compatible LCA - 6: Slide Mechanisms for Clean Room LCA

By システム管理者 on May 11, 2012 12:00 AM | No Comments | No TrackBacks

It is appropriate to consider that "There definitely will be particulate generation from locations where two sliding parts meet and slide together" from a standpoint of friction, wear, life of slide mechanisms. Therefore, the cleanliness technology for clean room LCA will be based on Item-2 of the "3 principles of cleanliness", < Do not generate contamination>.

There is a lubrication technology to reduce the issues of friction, wear, life and aging variations. This lubrication technology is also utilized for the clean room LCA equipment.

Cleanliness technology for slide mechanisms

The fundamental concept is to devise countermeasures for the following two main reasons of particulate generation from slide mechanisms.

a) Particulates generated by repeated sliding and wear of two objects
b) Splashes of oil/grease (see [Fig.1])

[Fig.1] Comparison of particulates by greases used on ball screws

From [Fig.1]

・	Since ball screws have rotating motion, they have great effects of splashing grease. In general, a lot of standard grease would be splashed for the first 20 hours, then the splashing would remain stable at high levels.
・	Low particulate grease would have small initial splash amounts and remain stable for long duration.
・	For both grease types, proper greasing maintenance is required. (see [Fig.2])

[Fig.2] Grease before and after the test

To reduce particulate generation of slide sections	Example of measures
Reduce sliding sections overall	Reduce usage of sliding/rotating/meshing mechanisms Example ・Sliding/rotating >> Non-contacting slides, etc. ・Meshing (gears, etc.) >> Reducing gears by servo mechanism usage ・Shorten transfer mechanism path
Reduce friction force	1.Reduce vertical loads >> Weight reduction designs by increased bearings to increase contact surfaces 2.Reduce acceleration and deceleration >> Reduce the effects of vertical load by reducing acceleration and deceleration
Suppress wear by lubrication	Clean lubrication usage and maintenance
Adoption of anti-wear parts	Adoption of bearings with ample specification margins. Use of ceramic balls, etc.
Suppress mechanical play and vibration	Suppress motion speeds and acceleration Optimized mechanism precision
Localized exhaust measures	Supported by mechanism structure Sealing of particulates by use of bellows