Today's safety lesson.....

[Chris Elston]

I thought this turned out to be an impressive catergory 4 safety circuit. I thought I'd share it with you guys. Today's drawing. DONE... finally... 1 SICK master safety relay and 5 SICK slave safety relays. The tech guys are going to have fun wiring this up!

[glaverty]

Gear damper, that rings a bell. Wouldn't happen to be for a company located in Frankfurt IL would it.

[Chris Elston]

Nah....your "seeing" things. I don't know what your talking about.

[Sleepy Wombat]

Question.. I noticed that E-Stop's are all wired in together...be aware that some safety consulants argue that this does not meat Cat 4 where others will because it is a general industry accepted practice.... However, i did also notice other input devices with the e-stops, but could not make them out...i would argue that this circuit would then not fully comply to Cat 4....An accumlation of faults does not lead to a loss of the safety function.. In fact i would say that it would only meet cat 2...with out any more detail..

[panic mode]

intersting topic.... it's raster bitmap so i can't make much out but it also seams that additional devices are using 1xNO and 1xNC contact... is that true or it only came out that way? also everything is on master relay, slaves are just expanding contacts. if this is true i would agree with SW that this is only Cat2 circuit. as for e-stops being stringed together, nobody here seam to care much about it (as long as e-stops are on separate controller) since they are manual function, dependant on human reflexes, used rarely and not intended or suitable to protect humans. it is different story when we look into safety devices like gates and light curtains (they are expected to remove hazard even if tripped accidentally, reaction time is very fast and independant from human reflexes etc.). common practice these days - everyone asks for cat-4... except e-stops... they can be cat-1, nobody cares. if there is need for cat-4 e-stop circuit, something else is not as safe as it should be. and if cat-4 e-stop is still requested by PHSR, E-Stops stringed together on one Cat4 controller can be argued to be Cat4 if it is found by PHSR that it is unlikely that more than one E-Stop would be pressed at the time (like when it's unlikely to have more than one operator run the equipment). I don't like the mess hardwired circuits produce, there are comparable if not less expencive programmable solutions (Pilz multi etc.) but customer always has the last word so things can look like this (30% of panel space is safety circuit):

[Chris Elston]

Wow panic mode, you got us beat! I guess one could argue the fact of Cat2. I was just trying to say I was having a little fun today. I know you European guys are hard to keep up with when it comes to safety circuits and designs. keep up the good work over there. (the european comment is directed at Sleepy, and all those people that follow the European guidelines). I know even some Canada companies that follow this to a "T".

[panic mode]

Hi Chakorules (and everyone else) Well, I'm not authority on safety issues, just trying to do my best. I like the topic as I expect more people to join so everyone can learn more from it (including myself). One thing is sure, safety is not too well defined and there are always different interpretations. Not everything can have number on it. One just has to see debates like what is "serious injury" when customer brings two contractors to do same PHSR. I was participating in different training sessions on the subject including robotics safety conference with safety circuit workshop. The circuit workshop was no doubt most interesting part. Some questions still went unanswered as time is always short and everyone tries to ask something about project they do. I wish I was allowed to post some of my work because i did tons of it and it's good to get feedback. However i can't do so because of policies and agreements i had to sign. I'm glad you are having fun. I like doing drawings too, but not necessarily safety circuits. This can be pain if one has to come up with decent protection when on a budget (like when it wasn't quoted properly). This is hardly problem nowdays as our sales dept got used to fact that safety can be expensive. We talk more about pricing for new projects.

[glaverty]

Nice to see that they won't be running their safety circuits through the PLC anymore.

[davefinic]

Panic mode one of your breakers has tripped

[Chris Elston]

[panic mode]

hehe, not mine, that one belongs to machine picture was taken during commisioning. part of the system was taken appart so i had to remove power until it's restored.

[Sleepy Wombat]

ANSI/RIA R15.06-1999 - 4.5.4 Control reliable safety circuitry shall be dsigned, constructed and applied such that any single component failure shall not prevent the stopping action of the robot.. 4.5.4.b Following a detection of a fault, a safe state shall be maintaned until the fault is cleared... Control reliability calls for redundancy and the prevention of a successive machine cycle under fault condition...These requirments are roughly equivalent to EN954-1 "Safety related parts of contol systems" risk assessment Cat 3 & 4.

[TimWilborne]

Is that a subtle way of saying part of it didn't work or had problems?

[panic mode]

well, things do happen, after all we make custom machines in record time, but this wasn't the case here. these babies have been running for days and tested in and out before shipment. it's just that some things had to be separated for transport. two small power cables between two cabinets are the only things that didn't have connector. everything was powered up and i was running it to train some people while our guys ware finishing installation. there was couple of maintenance guys to look at the safety circuit so i snapped few pictures and added text to complement documentation (posted pic is just small part i cropped for this topic).