safety controller -> PLC for cycle start

[multiplex]

Hello everyone,

I have a few questions i'm hoping someone can help with.

We have a fairly simple safety circuit

- two hand tie down
- light curtains
- gate latches
- e stop

I'm going to use one of the new Banner safety controllers (SC22) to manage all of the inputs.

My question is how do i then feed this to the PLC to function as a cycle start? Do i need to use two inputs on my PLC to maintain a 'safety' circuit? I would think using one input would undo all of the redundancy ahead of it.

Next question is in regards to servo drive - Specifically AB Ultra3000.

Upon a e stop situation, how do i interupt power to the motor? Is there a input into the driver for this? Do i place a set of contacts and kill power to the servo?

Sorry for the newbie questions - I'm just not getting quick responses on my questions from my venders

Thanks!

 

[PLC]

I would think using one input would undo all of the redundancy ahead of it.

Next question is in regards to servo drive - Specifically AB Ultra3000.



Have a look at Siemens and profisafe. Everything can be out on one wire with one progrm

It is very use to impliment too















Upon a e stop situation, how do i interupt power to the motor? Is there a input into the driver for this? Do i place a set of contacts and kill power to the servo?

Sorry for the newbie questions - I'm just not getting quick responses on my questions from my venders

Thanks![/QUOTE]

 

[mellis]

If your safety circuit is designed properly, it will operate completely independant of the PLC running the sequence. If you want to use an output from the safety controller to signal the PLC to start a sequence, that is fine. In that situation, the PLC is not part of the safety system and does not need to be redundant.

The servo is something you will have to work out with the owner and the vendor. Simply cutting power may not be safe. It depends on the situation.

Seems to me you need to take a step back and do risk evaluation and determine what the safety requirements are before you design the system.

 

[multiplex]

understandable - i'm waiting for a response from my vendor, so maybe that is the best bet.

What happens if the input of the PLC faults and falsely triggers a cycle start. Unlikely, but if the system up until that point is redundant i would think that would be the weak link. Just wondering how other people handle this?

The safety controller has two outputs per bank, which normally would go to a safety relay. So should i use those as my PLC inputs directly?

 

[kolyur]

The SC22 has status (non-safety) outputs that you can configure to indicate certain conditions to the PLC. However, as others have mentioned, the safety circuit should be independent of the PLC. If you provide more details about how the machine cycle has to operate, you may get more suggestions.

Concerning the servo drive, here is my recommendation:
Use one of the safety outputs on the SC22 to switch power to the PLC's outputs, which should include the Enable output to the servo drive. So, the servo will lose its enable and stop when the E-stop is triggered, independent of the PLC. Since the servo enable on the U3k is not safety-rated (as far as I know), use an additional SC22 output to drive a contactor located between the servo drive and its motor. Set it to off-delay mode so that when the E-stop is triggered, the contactor will open a short time after the enable is dropped (say 0.25-0.5 sec; depends on the emergency decel time setup in Ultraware) and provide a mechanical break for safety purposes. The Ultra 3000 install manual shows a contactor on the line side of the drive--I would not suggest doing this as frequent cycles of the line power will shorten the life of the drive, and you have to wait for it to power-up every time.

 

[mordred]

One note if the machine requires a class 3 stop ie a controlled stop then the input to the PLC will be required but there is nothing wrong with sending a status input to the PLC.

 

[kolyur]

What happens if the input of the PLC faults and falsely triggers a cycle start.

If your safety system is designed correctly, it shouldn't matter. All of the machine components capable of causing harm (motors, valves, etc) should be disabled if the safety circuit is off, so a cycle start signal from the PLC would have no effect.

The safety controller has two outputs per bank, which normally would go to a safety relay. So should i use those as my PLC inputs directly?

No. Those are redundant solid-state signals designed to be fed into a safety interface module like the Banner IM-T-9A. The relay outputs will then control power to contactors, starters, PLC output cards, and other devices that need to be safety controlled. As mordred says, you can have a status signal from the SC22 that tells the PLC whether the safety circuit is enabled.

 

[multiplex]

thanks for the feedback kolyur. I will check into the Ultra 3000 manual a bit.

the only reason the cycle start is tied into the safety system is the SC22 controller is used to create the logic for the two hand tie down. The SC22 has three safety rated outputs which can be assigned in various ways. It also has non-safety outputs.

Maybe a better question would be - how does one create a cycle start button on a machine with safety in mind

little back ground on the machine:

it is a hydraulic and servo driven 'trimming' press. The operator is located a few feet away from the actual press pinch point. The operator and other areas of the press are secured by hard guarding and two different light curtain zones. Along with that, the customer is requesting the cycle start be a two hand tie down.

we have had the Banner reps in, and they agree that our machine and components are a safe design - its just a matter of connecting all the pieces in a proper manner.

 

[mordred]

forgot to mention one thing make sure all signals that run things such as the motor are positive Ie no 0 volt activate this will prevent a short after the start switch or PLC output from false activating also if you tie in a status input from the PLC you can interupt the start rung

 

[multiplex]

thanks for those few replies that i missed there. I think that helps clear up alot of things.

 

[OZEE]

You CANNOT use the PLC as a part of your safety circuit, unless it's a safety-rated PLC.

Your safety circuit MUST be going to an MCR that will drop out the control power. Then it doesn't matter if the PLC false-starts... for whatever reason. You can have an aux going into the PLC to indicate an alarm status, but you cannot use it otherwise. The safety circuit must drop out a control relay...

 

[multiplex]

Yes i will have two control relays. One to drop out power to hydraulic pump and one for the servo (yet to be determined exactly how)

 

[Jeebs]

Late reply to the topic.

You could also add a 3rd contact to the two hand tie down. (2 contacts)
These go to the PLC.
These 2 contacts + the contact from the safety relay can be conditions to start the press.
With this you can add some other nice things. Like both tie downs need to be released before the press can start again. This to avoid clever operators from blocking 1 contact and thus only using 1 hand to operate the press.

 

[multiplex]

i think here is the plan moving forward.

Banner safety controller -> safety relay -> enable on Ultra3000

Depending on customer feedback, we will placed a delayed set of contacts on another safety relay for the power to the Servo.

Third safety relay to control motor on hydraulic pump

I think that should cover everything