Lets Talk E-Stops

I am designing a control system for a planar mill with nine RIO control stations. The production boss wants the E-Stops to only shut off the things controlled by each individual console. Other think that the E-stops should shut off everything controlled within view of the operator; so that if another operator gets caught in a machine within view of someone else the other person can push thier own E-Stop and save them.

I have only worked with E-Stops that shut off everything controlled by the PLC complete.

Are thier laws governing such?

What would be the safest way?

Is thier an industry standard for E-Stops for RIO?

Forgive my ignorance but I was put into this situation because someone got into a pinch. This would be only the fifth thing I've programmed; and I have never designed a complete system before.

All help would be greatly appreciated.

Thanks

Estops should be available to operators to prevent damage, personal injury, halt a malfunction due to equipment failures or operator mistakes, etc.

If you stop one part of a machine the previous part of the machine will need to halt anyway, so it can be stopped too, but not "safed" necessarily. Each case has to be analyzed as to what is best to do. To safe a pipe line I would fail-close the valve if appropriate, but if the concern was an overhead crane, then simply stopping the motors in place and applying locks/brakes is called for since a person might be under the crane (reason for Estop actuation).

You have to be aware of the local codes. For instance some areas require the use of special key/gate-latch sets for fencing around moving equipment. Insurance/Fire/OSHA approval will not be granted without the devices (no substitutes). When the operator removes the key to gain access inside the fence, electrical input causes an Estop type reaction.

If there are distinctly separated unrelated areas of accessibilty/control/motion/etc then separate estop zones could be appropriate. Lastly who will be the PE stamping the drawings? Because he and his company and others will be sued in the event of damage or injury, and that person needs to sweat the details. Its a serious assesment not to be taken lightly. The owner MUST also approve the plan or you should not procede with the integration, or allow mechanical designers to throw a situation in your lap that you feel is inherintely unsafe.

When I went from tire machines to locomotives, I lost a lot of exposure to safety regulations. If it was possible for someone to be hurt, I had to have a way to prevent it, and a way to stop it. This ranged from light curtains to pull ropes.

Locomotives were easy, all you had to do is figure how to make a panic stop.

I won't pretend to know the current laws, but it seems to me that you could have two buttons, one for "local" stop, and the other "all kill". I had used these 5 yearsa ago with great success. The local stop didn't have to be a big red mushroom, I think they were black, and passed some safety and insurance inspections witjout any problems.

Anyway, some food for thought...

regards.....casey

As Casey mentioned, there should be two types of stops...

plcman777 said:

The production boss wants the E-Stops to only shut off the things controlled by each individual console.

Click to expand...

These buttons would be labeled "STOP"

plcman777 said:

Other think that the E-stops should shut off everything controlled within view of the operator; so that if another operator gets caught in a machine within view of someone else the other person can push thier own E-Stop and save them.

Click to expand...

These buttons would be labeled "EMERGENCY STOP"

The production boss makes his point because many operators use the "EMERGENCY STOP" as a 'regular' stop.

beerchug

-Eric

Maybe I should have tried putting an "E-Stop" on a locomotive for the panic stops.

Hmmmmmmmmmmmmm...

regards.....casey

Train story for Casey...

So about a year ago I see an artical in the local rag about a historic preservation club giving rides for a buck on a newly partially restord street car. Hmmm. so I pile the kids in the car an take them to the depot where the street car is running from. Problem is no power wires running over the tracks. Solution buy an old locomotive, attach it to the street car and power the street car with the locomotive.. I expressed my doubts but the street car driver swears that the street car is pulling the locomotive...

I really like the two button idea. As a maintenance electrician I've seen it done a lot of places, I didn't think of it though.

I'll bring it up with all concerned on Monday and see what they think.

Keep the good ideas coming!

Thanks guys

The following I cut and pasted from the 2002 NFPA 79 "Electrical Standard for Industrial Machinery". I'm not sure what other codes and standards exist out there on this subject. Interpretation of this code will probably also vary, depending on your local AHJ or OSHA Rep. Hope this helps;


9.2.2* Stop Functions. The three categories of stop functions
shall be as follows:
(1) Category 0 is an uncontrolled stop by immediately removing
power to the machine actuators.
(2) Category 1 is a controlled stop with power to the machine
actuators available to achieve the stop then remove power
when the stop is achieved.
(3) Category 2 is a controlled stop with power left available to
the machine actuators.

9.2.5 Operation.
9.2.5.1 General.
9.2.5.1.1 The necessary interlocks shall be provided for safe
operation.
9.2.5.1.2 Measures shall be taken to prevent movement of the
machine in an unintended manner after any stopping of the
machine (e.g., locked-off condition, power supply fault, battery
replacement, lost signal condition with cableless control).
9.2.5.2 Start.
9.2.5.2.1 The start of an operation shall be possible only
where all of the safeguards are in place and functional except
for conditions as described in 9.2.4.
9.2.5.2.2 On those machines where safeguards cannot be applied
for certain operations, manual control of such operations
shall be by hold-to-run controls together with enabling
devices.
9.2.5.2.3 Interlocks shall be provided to ensure correct sequential
starting.
9.2.5.2.4 On machines requiring the use of more than one control
station to initiate a start, the following criteria shall be met:
(1) Each control station shall have a separate manually actuated
start control device.
(2) All required conditions for machine operation shall be met.
(3) All start control devices shall be in the released (off) position
before a start operation is permitted.
(4) All start control devices shall be actuated concurrently.
9.2.5.3 Stop.
9.2.5.3.1 Each machine shall be equipped with a Category 0
stop.
9.2.5.3.2 Category 0, Category 1, and/or Category 2 stops
shall be provided where indicated by an analysis of the risk
assessment and the functional requirements of the machine.
Category 0 and Category 1 stops shall be operational regardless
of operating modes, and Category 0 shall take priority.
Stop function shall operate by de-energizing that relevant circuit
and shall override related start functions.
9.2.5.3.3 Where required, provisions to connect protective
devices and interlocks shall be provided. Where applicable,
the stop function shall signal the logic of the control system
that such a condition exists. The reset of the stop function
shall not initiate any hazardous conditions.
9.2.5.4* Emergency Operations (Emergency Stop, Emergency
Switching Off).
9.2.5.4.1 Emergency Stop. Emergency stop functions provided
in accordance with 9.2.5.3 shall be designed to be initiated
by a single human action.
9.2.5.4.1.1 In addition to the requirements for stop, the
emergency stop shall have the following requirements:
(1) It shall override all other functions and operations in all
modes.
(2) Power to the machine actuators, which causes a hazardous
condition(s), shall be removed as quickly as possible
without creating other hazards (e.g., by the provision of
mechanical means of stopping requiring no external
power, by reverse current braking for a Category 1 stop).
Reset of an emergency stop circuit shall not initiate a restart.
9.2.5.4.1.2 Where required, provisions to connect additional
emergency stop devices shall be provided in accordance with
Section 10.7.
9.2.5.4.1.3 The emergency stop shall function as either a
Category 0 or a Category 1 stop (see 9.2.2). The choice of
the category of the emergency stop shall be determined by
the risk assessment of the machine.
9.2.5.4.1.4 Where a Category 0 stop is used for the emergency
stop function, it shall have only hardwired electromechanical
components.
Exception: An electronic logic (hardware or software) system as well
as the communication network or link that complies with both 9.4.3
and 11.3.4 and is listed for Category 0 emergency stop function shall
be permitted. The final removal of power shall be accomplished by
means of electromechanical components.
9.2.5.4.1.5 Where a Category 0 or a Category 1 stop is used
for the emergency stop function, final removal of power to the
machine actuators shall be ensured and shall be by means of
electromechanical components. Where relays are used to accomplish
a Category 0 emergency stop function, they shall be
nonretentive relays.
9.2.5.4.2 Emergency Switching Off. Where the emergency
switching off function is used, it shall be initiated by a single
human action.

Thanks for posting that CT782. I didn't know NFPA was available in electronic format. I only have the paper version...

Of course, all the requirements are important, but I feel this part should be emphasized:

Reset of an emergency stop circuit shall not initiate a restart

I find this one is ignored all to often...

beerchug

-Eric

Eric,

Most of the NFPA code texts are available in PDF or Paper format. The PDF is encrypted so that you can only open it if you have a connection to the net and are logged into NFPA under the account you used to purchase the PDF. It will allow you to cut and paste up to 50 selections per day from the PDF. I like the search capabilities of the PDF and simply printed copies and put them in binders for searching with a computer-monitor-migraine. =o)

Here's the link if you're interested.

http://www.nfpa.org/catalog/

Best Regards,

Chris

Thanks for the info, Chris. Interesting concept they have with the protected PDFs. I find it odd that they charge the EXACT same price for the PDF as the paper version. Seems a bit steep for a PDF, since the book is only like 100 pages.

I may consider the PDF for the 2005 NEC. In that case, the search ability would be REALLY handy.

beerchug

-Eric

The types of stops and their Labels are dependent on what the stops are used for. For instance, we have conveyor layouts in our plant that we have Zone Stops for. The E-stop in still inplace but the Zone Stop kills only part of the line, not all of it. Operators are trained to know the difference in the two. The Zone Stops are wired to the plc in some cases, the E-Stop kills all 3-phase to the motors and the 110vac to the output cards.

I have seen a lot of E-Stop buttons that will shut down a process, to killing power to the whole room(every training room I've been in) with the exception of the light, to killing power to the machine.

One such machines, if you hit the E-Stop, it killed power at the main contactor but if the spindle was running it didn't apply the brake to the motor, so you didn't have power to the machine but you had a motor turning 3600rpm with two diamond wheels on it. Stick your arm in the door and pull back a nub.

The main thing is make sure the operators or anyone that will be in the area(plant managers included) know the procedures to the equipment, and what E-Stops affect what.

Martin T. said:

One such machines, if you hit the E-Stop, it killed power at the main contactor but if the spindle was running it didn't apply the brake to the motor, so you didn't have power to the machine but you had a motor turning 3600rpm with two diamond wheels on it.

Click to expand...

That sounds very strange.
Brakes that provide safe standstill should engage when you remove the power - not the other way around.
Was the braking done via a VFD, or some other electronic way ?

It's been awhile since I messed with the machine, it was a 7AA Strasbaugh Grinder, I believe the braking was done by the drive. Why they had it set up like that I'm not for sure. It's just one of those things you haad to let the operators know about.