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Author Topic: Configuring a light curtain for a CNC router  (Read 462 times)

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Configuring a light curtain for a CNC router
« on: July 16, 2018, 04:55:40 AM »
I am setting up a CNC router, 2500x1800 mm, with a linear ATC running on a CSMIO IP-A controller. I will surround the machine with safety light curtains to make the machine safe to use according to EU Machinery Directive. However I am not sure what is the best way to implement such a safety feature.  What is best practice on this area?

Is it sufficient to let Mach4 go into feed hold and turn off spindle if the light curtain is triggered? Or should the machine go into E-stop mode and disable power to the servos and spindle?

My main concern is that I will need to be inside the curtains for setting up the work piece while jogging the machine with the hand wheel. Is this considered "unsafe" if I limit the max allowed rapid speeds while being inside the curtains?

Thankful for any input on this.

Offline Tweakie.CNC

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Re: Configuring a light curtain for a CNC router
« Reply #1 on: July 16, 2018, 05:42:03 AM »
There are dangers with operating any form of equipment and you perhaps need to decide just how safe you need to make your machine environment.

If you or any part of you is inside the curtain at any time whilst the machine is active then you are not ‘totally safe’.
Even at (perhaps ‘especially at’) limited, slow speeds the available torque of any axis could still cause substantial personal injury.

I take a ‘calculated risk’ when operating my machines. I have an Emergency Stop (which instantly disconnects power to all parts of the machine and accessories but not the PC) and a dry powder Fire Extinguisher (especially for laser work) within easy reach at all times. Third parties and pets are not allowed anywhere near an operating machine. So far, this has served me well but, as you can see, it is not foolproof and it is not totally safe.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline ger21

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Re: Configuring a light curtain for a CNC router
« Reply #2 on: July 16, 2018, 07:19:02 AM »
Quote
Is it sufficient to let Mach4 go into feed hold and turn off spindle if the light curtain is triggered? Or should the machine go into E-stop mode and disable power to the servos and spindle?

If you want to follow the EU Directive, then you have to go by their rules, whatever they may be. I doubt that going into Feedhold is sufficient. I also doubt that you can be inside the curtain while jogging.
Gerry

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Re: Configuring a light curtain for a CNC router
« Reply #3 on: July 16, 2018, 07:45:51 AM »
The thing with that directive is that it doesn't state any very specific requirements. It is up to the machine builder to decide what is safe for the user of the machine. However I found this document now with some guidelines. http://www.hse.gov.uk/pubns/wis22.pdf

But it is still interesting to hear what your experiences are when i comes to safety for the operator.

Offline ger21

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Re: Configuring a light curtain for a CNC router
« Reply #4 on: July 16, 2018, 08:25:00 AM »
I've been using big industrial Italian made routers for over 20 years. I've never used one with light curtains, but the ones with safety mats don't allow you to jog the machine while standing on the mats, and stepping on the mats during operation will disable power to the machine. I'm assuming that the light curtain should function like the mats do.
Gerry

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Re: Configuring a light curtain for a CNC router
« Reply #5 on: November 29, 2018, 10:19:13 PM »
I'm currently working on this setup and this is what I want to happen when the curtain is triggered:
- Stop a running program
- Spindle start not allowed
- Limit max allowable speeds
- Disable JOG, CYCLE START and SPINDLE START buttons
The intention is that after the light curtain has been triggered it can only be moved by the MPG handwheel, and it will be necessary to "reset" the curtain from a button within mach4 to allow the machine to work normally again.

However, are any of you aware of a way that I can the disable the spindle and limit the feed rates? Are there any pound variables or other ways to set these? And are there any way to disable the buttons in mach4?
Thanks for any input.
Re: Configuring a light curtain for a CNC router
« Reply #6 on: November 30, 2018, 10:24:30 AM »
Jorgenbli;

Assuming this is or will be a commercial machine(??)

Three thoughts;

1) Making it "safe" is different than making it comply with a standard.  Which is most important to you depends on how/ who/ and where the equipment will be used.

2) Here in the USA there is a consortium of control experts that work together to interpret the standards.  Their interpretation changes over time while the standards remains fairly unchanged. These are the experts whose control schemes you will wish to follow - as opposed to you interpreting the standard.  Their guidance is usually considered "best available control technology" or some such language and will stand up should anyone ever do something that gets someone hurt.

3) Here in the USA, companies are doing more over time to simply keep humans out of the machine's envelope.
Think fence as opposed to light curtains.
Think E-Stop as opposed to Control Stop...

If the control scheme you propose was to be used this side of the pond, you would have to develop a FMEA (Failure Modes Effect Analysis), or similar study to show that the machine still met intent of the standard should someone be in the controlled space while slow-jogging a powered machine.

You are heading in the correct direction by asking the good questions.

-MDog
Re: Configuring a light curtain for a CNC router
« Reply #7 on: November 30, 2018, 04:10:46 PM »
Thanks MadDog,
The machine is for my company and will be operated by others than me. The main goal is to avoid anyone getting hurt by it. At the same time, it should be possible to operate it to set work zero etc easily while being inside the curtains. I know on CNC mills it is usually possible to jog the machine with the main door open, and even run the spindle at low rpm.
Re: Configuring a light curtain for a CNC router
« Reply #8 on: November 30, 2018, 05:22:05 PM »
 jorgenbli;

This is really not something that should be done without understanding the consequences.    I suggest you design what you think is appropriate then use the services of a commercial organization that is expert in this area to validate the design and performance before it is built.

I did do some light digging tho:
I AM NOT SUGGESTING THESE ARE CURRENT STANDARDS/ best practices:

Assuming by the link you sent you are in the UK...

See Page 5: http://www.hse.gov.uk/pubns/wis22.pdf  This probably requires a two-hand control to still ensure the operator cannot be in contact with or impacted by anything that moves.  There is a good list of references at the end of the article.
Some of these likely have the authority of law in the UK: Safeguarding

 A, B, and C level standards

Yeah, it gets overwhelming pretty quick.