Can light curtains be wired into a PLC?

[Guinness]

I thought this AB link would be helpful for designing a light curtain system.

Safeguarding Applications and Wiring Diagrams
http://www.ab.com/en/epub/catalogs/3377539/5866177/3378082/3384396/tab22.html

 

[cschmid]

petersonra I do agree that there is several options..Jim has a good plan here and would work nicely..you also do need to address why the operator would need to stick his hand in the machine and also why he would do it again and risk another injury..I believe here you could use the curtain for couple of purposes and use it through a plc..I believe you are on the right track..what would really be nice is actually what the process is that we are talking about..like what is it you are manufacturing..

 

[mutabi]

The Process:

We take lengths of straight copper tube (1 inch in diameter up to about 25 feet long), and fin them. i.e. run them through some disks which cut into the tube and raise up fins, which improve the heat transfer capability.

How it works. We load up the machine with 100 pieces of straight copper tubes. We have two rods and insert the tubes into the machines to be finned. While one is finning, the other one is being loaded with a new blank tube. We have a simple DC motor which runs a belt operated pusher which pushes the blank tube onto the empty rod while the other one is finning. If for some reason the tube is bent, it will have to be guided onto the empty rod. Its possible to use something other than your finger to do that.

When the machine has stopped finning, the rods rotate vertically, and now the new blank tube is pushed up into the machine using a pneumatic air cylinder, where it gets finned, while the other, now empty rod gets loaded with a new blank tube. Again, if the tube is bent, even slightly, it will hit the sides of the machine has it is being pushed up into the machine to be finned.

The other reason they stick their hands in there, is to changing tooling on the rod. They should be doing this locked out, but they dont. So instead of making them lock it out, we have to engineer around their stupidity/laziness.

 

[cschmid]

makes more sense now..Thank you..

 

[pfalcon]

You have several major errors as you have described your machine. Please review NFPA79-2007 before you proceed.

1) When tripping an Estop circuit you must stop all hazardous motion. This means that clamps should not change state when the power is killed due to an Estop, ram heads must not drop, etc.

2) You are reaching into a hazard area therefore the light curtain must guarantee safety - not an Estop. This is typically done with "muting". The light curtain must be clear OR the machine motion must be secure. The light curtain must be "hardwired" with the "muting" to guarantee safety against the protected motion. Not necessarily the Estop.

3) All safety issues must be protected by safety rated equipment. Until the NFPA79-2007 this meant that you could not use a PLC at all as a safety device. Now you can use safety controllers as long as access to their programming is properly restricted. A standard PLC cannot be used with the light curtain. The safety controllers are the only legitimate "softwire" permitted.

Please respect the NFPA79 as you would respect the NFPA70.

Estops are covered in NFPA79-2007-9.X
Stop categories are defined at 9.2.2
Category 0 is immediate uncontrolled removal of power to actuators
Category 1 is controlled stop then removal of power to actuators
Category 2 is controlled stop with retained power to actuators
Estops are category 0 or 1 and stated at 9.2.5.4.1 and determined by risk assessment
Light curtain category is 0, 1, or 2 as determined by risk assessment

A light curtain may use the Estop circuit.
A light curtain is not required to use the Estop circuit.
A light curtain usually does not use the Estop circuit because we normally want a category 2 stop.

As stated in an early post if you wish to use a controller with the light curtain you may use any controller that is safety rated. They usually are marked in special colors like red. According to NFPA79-2007-9.4.3.2 there are additional restrictions on programmable devices.

 

[petersonra]

Please respect the NFPA79 as you would respect the NFPA70

Generally speaking, compliance to NFPA70 is a legal requirement. That is not generally the case for NFPA79, although one could argue it is implied by OSHA.

 

[pfalcon]

Generally speaking, compliance to NFPA70 is a legal requirement. That is not generally the case for NFPA79, although one could argue it is implied by OSHA.

Actually OSHA is very clear on this issue. OSHA has its own standards and states if they are insufficient you are still liable. They state that their standards are known to be inferior to industry standards. They recommend that you adopt industry standards in place of OSHA standards. Once your company adopts an industry standard then OSHA will hold you to them. They are at that point a legal requirement for your company.

 

[cschmid]

very true statements..yet the only enforcement that is normally available is the installer them selves..So it is to your benefit to do the highest quality of work possible..the only time OSHA will enforce any of these rules is 1) on a surprise inspection ( which is really low) 2) when one of your co-workers is hurt or killed..I would not want the second one on my conscious..

 

[weressl]

Generally speaking, compliance to NFPA70 is a legal requirement. That is not generally the case for NFPA79, although one could argue it is implied by OSHA.

A​

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PPENDIX A TO SUBPART S OF PART 1910?REFERENCE DOCUMENTS​

does lists 70, 70E atc., but it does NOT lists NFPA 79.​

 

[IMM_Doctor]

Team Survey

Team Survey

Please don't look for one magic code or standard to resolve the issue. Have all affected parties sit down and discuss the situation.

Operator
Supervisor
Manager
Maintenace
Controls Engineer
Safety Coordinator
(Corporate Insurance Provider)

Do a risk assement, Injury? How Bad, How Frequent?
If an operator is risking injury every machine cycle, then monies should be spent on safety devices to mitigate risk.

You may not need to E-Stop the entire machine on a light curtain breach, but merely interrupt the axis that would cause inury. IIf this is the case then the single channel PLC input would be a bad choice, as a single compnent failure could lead to injury.