pneumatic cylinder control safety -...
TRANSCRIPT
Pneumatic Cylinder Control Safety
Eric Cummings – ROSS CONTROLSGlobal Industry Manager - [email protected]
803-622-1161
19 June 2013 www.rosscontrols.com 1
Agenda Ross Controls Introduction
Cylinder control basics
Safety control basics
What is the best solution?
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The ROSS Controls Story Founded in 1921 by Charlie Ross Design, manufacture and sale or pneumatic valves and systems for
industrial equipment 1954 – First double valve ever developed by ROSS 1962 – Developed first pneumatic energy isolation device 2005 – DM2 ™
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Global Facilities
ROSS Controls - Madison Heights
ROSS Controls - Troy, MI ROSS UK Ltd.
ROSS Asia - Japan
ROSS Europa GmbH - Germany
ROSS Controls - Lavonia, GA
ROSS South America ROSS IndiaROSS China19 June 2013 4
Safety IndustryCurrent Committees with ROSS
RepresentationANSI Z244 Control of Hazardous Energy - Lockout Tagout
ANSI B11.0 General Safety Requirements & Risk Assessment
ANSI B11.1 Mechanical Power Press
ANSI B11.2 Hydraulic and Pneumatic Presses
ANSI B11.19 Performance Criteria for Safeguarding
ANSI B11.26 (Former TR6) Safety Control Systems for Machine Tools
ANSI B155.1 Packaging and Packaging Related Converting Machinery
ANSI B11.151 Plastics Machinery
CSA Z432 Guarding of MachineryCSA Z460 Control of Hazardous Energy - Lockout - Tagout
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Risk Assessment
Other standards requiring risk assessment:
• CSA Z432
• ANSI B11.0
• ANSI B11.19
• RIA 15.06
• ANSI/PMMI B155.1• ISO 13849
B11.0 Safety of Machinery General Safety Requirements and Risk Assessment
Task Based Hazard Analysis
Determine:
• People exposed
• Tasks required
• Severity of hazard
• Exposure to the hazard
•Consider:
•Foreseeable misuse
•Failure modes
Risk Assessment
Cylinder Control BasicsSpring return cylinder
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Double acting cylinder
Cylinder Control Basics
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What are the applications?• Automation• Packaging• Palletizing• Stacking• Cylinder presses• Tensioning• Winding• Cutting• Doors
Any linear motion requiring force.
Cylinder Control BasicsSpring return cylinder• Force = pressure x area – spring force• Speed function of air supply flow rate
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Cylinder Control Basics
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2
Single Acting Cylinder Retracted
Spring return cylinder
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3 1
2
Single Acting Cylinder Extended
Push
Cylinder Control BasicsSpring return cylinder
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Cylinder Control BasicsSpring return cylinder - vertical• Force = pressure x area – spring force + gravity• Speed function of air supply flow rate
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Cylinder Control Basics
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2
Spring return cylinder safety issues:• Speed control extending
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Cylinder Control Basics
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2
Spring return cylinder safety issues:• Speed control retracting
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Cylinder Control Basics
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2
Spring return cylinder safety issues:• Speed control extending and retracting
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Cylinder Control BasicsSpring return cylinder risk assessment
Risk Result
Inherent motion De-energizing causes return motion
Cylinder spring breaks Cylinder does not return
Valve sticks open Cylinder continues moving or does not return
Valve sticks closed No motion
Speed of tooling Motion too fast or slow
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Cylinder Control Basics
13
2
Spring “extend” cylinder safety issues:• Speed control extending and retracting
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Cylinder Control BasicsSpring “return” cylinder risk assessment
Risk Result
Inherent motion De-energizing causes extend motion
Cylinder spring breaks Cylinder does not extend
Valve sticks open Cylinder continues moving or does not extend
Valve sticks closed No motion
Speed of tooling Motion too fast or slow
What is the function and the risk if that function does not occur?
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Cylinder Control Basics
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Double acting cylinder• Force right = pressure x cylinder area• Force left = pressure x (cylinder area – rod area)• Speed function of air supply flow rate
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2
3
4
Cylinder Control Basics
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Double acting cylinder• 4/2 spring return valve
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4
Cylinder Control Basics
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Double acting cylinder• 4/2 spring return valve
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4
Cylinder Control Basics
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Double acting cylinder• Limit flow (speed) into one end
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3
4
Cylinder Control Basics
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Double acting cylinder• Limit flow (speed) into both ends• Can cause jerky motion
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3
4
Cylinder Control Basics
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Double acting cylinder• Limit flow (speed) out of both ends• Only works with back pressure present
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3
4
Cylinder Control Basics
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Double acting cylinder• Limit flow (speed) out of both ends• Limits flow (speed) into cylinder after lockout
Cylinder Control BasicsDouble acting cylinder risk assessment (4/2 spring return)
Risk Result
Inherent motion De-energizing causes return motion
Valve sticks open Cylinder continues moving or does not return
Valve sticks closed No motion
Speed of tooling Motion too fast or slow
Reapplication of air Rapid motion could result after lockout
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2
3
4 Power
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Cylinder Control BasicsDouble acting cylinder• 4/2 detented valve
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2
3
4Power
Cylinder Control BasicsDouble acting cylinder• 4/2 detented valve
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Double‐Acting Cylinder Retracted
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2
3
4
Jam Example
UNEXPECTED MOVEMENT
JamPinched
Cylinder Control Basics
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Cylinder Control BasicsDouble acting cylinder risk assessment (4/2 detented)
Risk Result
Inherent motion Motion does not stop until stroke completed
Valve sticks Cylinder continues moving or does not return
Pressurized cylinder Rapid motion after jam cleared
Speed of tooling Motion too fast or slow
Reapplication of air Rapid motion could result after lockout
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1 35
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24
1 35
241 35
5/3 Closed Center
5/3 Open Center
5/3 Power Center
Cylinder Control Basics5/3 directional control valves
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1 35
24
Cylinder Control Basics5/3 Closed Center
Risk Result
Valve sticks Cylinder continues moving or does not return
Trapped pressure Must be addressed
Trapped pressure Rod side has less force
Center position untested Normal operation may not use center function that is depended on for the safety function
Rapid motion Will result after lockout, if trapped pressureremoved
Speed of tooling Motion too fast or slow
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Cylinder Control Basics5/3 Open Center
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1 35
Risk Result
Valve sticks Cylinder continues moving or does not return
Inertia & gravity Cylinder continues moving
Center position untested Normal operation may not use center function that is depended on for the safety function
Rapid motion Will result after lockout, if trapped pressureremoved
Speed of tooling Motion too fast or slow
Cylinder Control Basics5/3 Power Center
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Risk Result
Valve sticks Cylinder continues moving or does not return
Trapped pressure Must be addressed
Trapped pressure Rod side has less force
Center position untested Normal operation may not use center function that is depended on for the safety function
Rapid motion Will result after lockout, if trapped pressureremoved
Speed of tooling Motion too fast or slow
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Cylinder Control BasicsRodless cylinder• Equal force on each side of the piston
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Cylinder Control BasicsLoad Holding - Pilot Operated Check• Traps pressure in the cylinder for load holding• Removal of trapped pressure
• Automatic• Manual
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Cylinder Control BasicsLoad Holding - Pilot Operated Check
Risk Result
Control Valve sticks Cylinder continues moving or does not return; pilot operated check non-functional
Trapped pressure Must be addressed
Load Holding
Cylinder brakes are applied by removing the air pressure Rod brake – stops a moving load
Rod lock – holds load in placeHazard
Direction
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Cylinder Control Basics
Perform a risk assessment• Pneumatics is one of the energy sources• Must consider:
• Failure modes• Foreseeable misuse
Safety Control Basics
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Two primary desired results:
1. Remove fluid power pressure to prevent movement and a hazard (remove motive force)
2. Trap fluid power to prevent movement and a hazard or use mechanical means
Safety Control Basics
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Fluid Power Exhaust Circuit
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•What is considered severe?
• Per EN 13736 & B11.2 there is a risk of injury if:Force > 150 N (33.8 lbf)Weight of tooling > 15 kg (33 lbs)
• Requires redundancy and/or monitored restraint
Safety Control Basics
Bore " Area Force (100) Force (80)
0.313 0.0767 7.7 6.1
0.438 0.1503 15.0 12.0
0.563 0.2485 24.9 19.9
0.750 0.4418 44.2 35.3
0.875 0.6013 60.1 48.1
1.063 0.8866 88.7 70.919 June 2013 www.rosscontrols.com 43
5/2 CROSSMIRROR Dual crossflow spool valve Faults to known output condition Check valve on inlet Fault indicator
Cylinder Return Function
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Hoze Failure• Senses hose failure & reduces flow to a safe level• Prevents hose whip injury & damage
EU 983-1996/5.3.4.3.2 requires all hoses tubing to be guarded or protected in case of failure
30 CFR 56.13021 & 57.03021 US Mine Safety & Health Administration requires guarding or protection on all hoses ¾” or larger
ANSI GSR - 2008 7.11 Machine design shall minimize potential hazards from: Sudden hazardous movement of a hose resulting from leakage or component failure
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What can be done to address pneumatic hazards?
Remove the motive force – exhaust down stream air
Selectively trap pressure if needed Provide way to remove pressure
Use mechanical devices when required
Maintain the Control Integrity of the safety system
Safety Valves
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Pneumatic Cylinder Control Safety
Eric Cummings – ROSS CONTROLSGlobal Industry Manager - [email protected]
803-622-1161
19 June 2013 www.rosscontrols.com 47