Safety PLC and scantime

[Mechamania]

Hi

For a new machine I would like to use a Safety PLC.
But the machine includes fast moving axis. So I would like to have a very short scantime. Preferable below 10 mS.
Is this possible?
Which PLC could I use.
What can I do to improve the scantime?
When I use remote IO over a safety ethernet protocol, does it influence the scantime a lot?

Any remark on this is very helpful for me! Thanks.

 

[shooter]

safety and scantime are not related,
if you need safe operation you have to feed back if something is moving. not a command stop but actual if it is moving, or in safe position etc.
scantimes are usually 10 ms as the whole program looping all the time.
if you need faster response have a look at arduino or any other embedded system.
and yes ethernet is influencing the speed as it needs a lot of feed back to see if message arrived etc.
btw i live in s hertogenbosch

 

[Mechamania]

Thanks Paul,

I heard that Safety PLCs are much slower than standard PLCs because they do a lot of internal checking.

 

[OzRoo]

There a couple of Possibilities here if you are using a PLC like Allen Bradley, Siemens or Omron etc that has a Safety module facility is one way to go, alternatively if the safety isn't complex just have a smart Safety relay like PilZ make or dedicated Safety PLC handle all the safety with the number crunching in the main PLC. All the Main PLC needs is usually some simple IO info to know which zones are on or off. You need to also consider redundancy as using a $8k Saftey Wizz bang PLC might not be easy to replace in a hurry if it goes down compared to $5k PLC & $4k Safety Controller. Also consider your software costs as you pay extra to get Safety Ladder capability on some brands. Also consider SCADA read/write access if relevant to both PLC & Controller
We've had a Siemens 319F S7 PLC with 8 zones of safety IO in the Rack on one production line, the 319F is about 10x faster than the 315F we replaced and has identical specs to a non-safety 319. We also have an Omron running parallel to a Pilz Safety PLC on another line with 11 zones of Safety and I prefer the later myself. But mainly because high end Siemens stuff is hard to get in Australia. And Siemens is such a pain to work with compared to Omron & Mitsubishi.
The Pilz guy seling us the Safety PLC skyped on how fast it was and what it could do etc, but when we read him the specs of the main PLC we were using the Safety PLC was way under spec to handle the number crunching, encoders & VSD positioning we desired. The top line Pilz was not in the same league as a high end Omron or Siemens or AB, but it depends on what you want also bearing in mind dedicated safety PLC's require learning their own language quirks.

 

[Mechamania]

Thanks OzRoo

What is the scantime or troughput you got with those safety systems?

 

[OzRoo]

Thanks OzRoo

What is the scantime or troughput you got with those safety systems?

I really don't remember, the Omron is newer by 4 years, we actually had to slow the Program down on the Siemens when we upgraded PLC's to every 60th scan because it was badly written and couldn't execute reliably. The Omron program was written by a better programmer and didn't have that issue.

But it's a bit subjective because it depends on what your PLC is doing compared to what ours is doing. Both machines are slightly different one making garage door panels the other roller doors from sheet coil, so basically operated a decoiler, pit sag loops, main feed roller, guillotine, press, conveyors & rollformers. Many of the drives are using 13bit encoders and VSD's for positioning. The press is a 6m wide 100tonne beam press with the PLC controlling the levelling by an encoder at each end and variable speed valving. We have multiple safety zones so we could be loading a coil in one zone, or enter the light curtains in the press etc without stopping product moving in other zones. Both are capable of basically making roughly 100 garage doors in 7 hours.