overriding a safety curtain?!?

Reading through the work orders today I came upon a request to setup a disable for the safety curtain in order for the quality engineer to do required setup on a 8 ton press. After investigating, the intended condition would allow him to leave actuators and clamps in the desired position without retracting when the curtain is broke. Obviously, this curtain was installed to protect the operator entering the area when theunit is cycled. My question is, if an organization makes the decision to allow certain "authorized and trained personnel" to bypass safety devices for setup and repair, what is the best way to tackle this? My first reaction was a maintained key switch inside the cabinet that basically "tricks" ignores or mimicks the input from the safety controller output. In addition a beacon light would run until the switch was returned to a safe operating condition. This is a Minotaur MSR6R/T from AB and there does not appear to be any muting or disabling option.

We use maintained key switches on our equipments which require setup by engineers. I program the logic to only allow inching/jogging of the equipment when the key switch is ON and also display a message on a message display unit which indicates that the equipment is in setup mode.

WrongWay,

1. Will the bypass switch allow the press to cycle?
2. Can someone get injured if the press cycles in bypass?
3. Can the setup man / next operator be injured if the press
cycles in bypass if the quality guy forgets to turn the
bypass switch off?
4. if the press cycles in bypass, what machine damage can
occur?

if you answered yes to 1, 2, or 3, and not knowing your setup fully, this is a decision that must be left up to safety, corporate management, and the legal department. Get signed approval and keep a copy for your protection.

OSHA will love this if someone gets hurt. with no records,
guess who is the fall guy.

Years ago, that little work order i had signed for doing something similar saved the company i worked for from bankruptcy and kept my rear out of trouble. the one who authorized that little change got fired and the company he worked for had to foot a multi million dollar bill plus legal
fees.

regards,
james

Could you install an enable switch (deadman switch)?

http://www.schmersal.net/Bilddata/broschue/b_zb_p02.pdf

WrongWay said:

Reading through the work orders today I came upon a request to setup a disable for the safety curtain in order for the quality engineer to do required setup on a 8 ton press.

Click to expand...

How are they accomplishing the required setup right now?

Could it be beneficial to change the valving of the actuators in question so that they stay put (but release pressure) when the light curtain is broken or power is taken away (think changing to 3 position open center valves)?

I would make sure to investigate this very very thoroughly before making any changes and get everyone involved in the decision making process, especially those qualified to perform a safety analysis.

Often, requests are made with the mentality of "Gosh, if we did this it would make my job easier" without fully examining all the consequences and alternatives.

There might be something you can do to accomplish the desired end result without compromising the safety controls.

Why do your actuators retract when you brake the light curtain. Would it not be safer if they stayed in there current position anyway?

Firstly, I whole-heartedly agree with James about covering your rear and getting something in writing and signed before you do this mod.

Also agree with Viks that you should have something in place to prevent the machine from cycling when the guy is in. Something like a castell/fortress key switch whereby the inspection guy would keep one of the keys on him during the inspection and the machine couldn't be started without it. Although this would mean quite a bit of work to incorporate this into the existing safety cct.

;-)

On a small mechanical Press it is Common to need to operate with out guard function.
There is a safety "Back emf" Motor monitor.
Normaly this would be used - It can pick up that the motor is almost Stopped thus allowing a slow Jog Process
At that time I would suggest allow the bypass of Light curtains.
AT NO OTHER TIME.

You need to get the Work request Author to Submit a written Notification that He/She accepts full responsibility for any injuries such a modification may cause.
For all time - SOME ONE WILL SUE SOMEONE
And you need to be proected.
Guarding is there due to risk AND
Mechanical Presses have a common historic record world wide
to remove peoples fingers arm and lives.
SO a work request should be ignored Unless the person issuing has Big dollar public liability.


THE PRINCIPAL IS SIMPLE
IF SOMEONE CAN SOMEONE WILL.

- I have had an Afternoon shift Production supervisor Cut the connecting chain on two Castelated locks
These bridged the rear light curtains.
the idae was to remove a metal blank from the rear of a blanking die 500t Mechanical Press.
Rather than fixing the actual problem.

That sounds like an application for "Trapped Key Switches", configured to severely limit machine functionality when the key is moved from the Run station to the Setup station.

We use them on all of out HV Test vault doors and controls.

The only thing to be sure of, is that ONLY ONE CODED KEY IS AVAILABLE ON THE FLOOR. No exceptions.

I believe safety should be first , it doenot matter how much you save in production or money , safety should be number one , can never be by-passed under any circumstances, how about if that light is blown and the key was forgot in bypass mode , and he start cycling and someone was at the back side repairing something inside the press which the operator could not see him!
so please , when you do any modification you have to think what would happen after 5 or 6 years or even if the machine is sold out with your nice bypass to someone else which does not know what you did.
thanks

adel1961 said:

I... light is blown and the key was forgot in bypass mode , and he start cycling ....

Click to expand...

That is one thing that trapped key systems prevent. The key must physically be moved from one position to another, if it is left in the 'setup' position, only setup functions are available. If it is moved to the run position, all run functions and safeties are available.

If a light curtain fails, it's default fault mode should be to make the system safe. If not, it was not configured correctly.

rdrast said:

The key must physically be moved from one position to another...

Click to expand...

That's what I was meaning when I mentioned the "castell" key system. We used to have one that worked well. 3 keys. You turned the 'X' key to release the 'L' key (they had letters marked on the bottom of them) and then used the 'L' key to release the 'T' key. The person working kept the 'T' key on them at all times.

The remaining keys were automatically locked into position until the 'T' key was turned which released the 'L' key etc etc.

We used to remember the order with the acronym 'X'tra 'L'arge 'T'... actually, it doesn't matter what the acronym was... the main is that the system worked!

The 'Castell' range is no longer available in Australia
We have the Fortress range, Haake, there are others.
it was easier to reffer to a captive Key type.
The problem of bridging guards will always raise questions.
The automatic Or Usual operation of a machine should not need bypassing. This is why I suggested the Motor Safety device.
This prevents the auto operation and prevents production.
That is important because there is no way they can run in an unsafe manor.
However the Most dangerous operations on a Press are both Job/Die Installation/Removal And Maintenance operations.
That is why I said Risk analysis.

We have installed bypass keys on our press light curtains because someone realized that if an operator got caught in a die, they would be standing in the light curtain. If the press was from 0-180 deg you would not be able to reverse the ram direction with the light curtain blocked. Only a select few keys are available and they are never used to assist in setup or quality issues. Also, they are captured keys that turn on a beacon when active and will only allow the press to cycle once without the press control reset being pressed or the key being returned to normal state. How are these tasked being performed now with the light curtains active? If they are asking for a bypass simply to make things more conveinent or the setup quicker, these are not good reasons to bypass safety devices. Also, before installing the bypass keys I got a signed letter from the plant manager releasing me of liability. To date these keys have never been used.

How does an operator get caught fro 0 to 180 Degrees if the light curtain is working
it is possible but there is a problem with the guard setup.

It is also possible to do a 1 off bridge to free someone
But not nesecary to set it up permanently - Isnt it.