Safety relay circuit diagram for a robot cell. Please Help

[Didawdidaw]

so i have been given this diagram and no explanation on what nay of it does, its for a safety relay for a robot cell it says this:
'Safety relays can made up of 3 relays (CR1-3) to ensure redundancy and cross monitoring, and can be applied to the following applications: ■ Emergency Stops ■ Light Curtains ■ Three Position Devices ■ Interlocked Gates/Hatches ■ Magnetic Switches ■ Light Beams ■ Safety Mats ■ Contact Strips ■ Foot-Operated Switches'

I'm assuming that the CR = is a relay safety device like a light beam?
I'm not to sure what '=/' is suppose mean, its never been explained to me. I assumed that when power goes threw it disconnects stops power to that relay?
I don't know what the squares mean before pretty much everything with 'A1X' 'A1Y' and so on I'm assuming that its nothing and just a way to identify things but i could be wrong.

So this is how I'm currently reading the circuit:
When start button is pressed CR1/2/3 activate and power up. I'm going to assume CR1 is a light sensor which when the beam is broken the machine stops, I'm going to assume CR2 is a magnetic switch on the door; when open breaks the circuit and stops the machine and then CR3 is a interlocked gate what will only open when there is no power to the machine. When the start/reset button is pressed it resets CR1/2 but CR3 stays active because its needed to so that entry can't be obtained whilst this happens (I'm reading this from the reset/start line on the circuit). When the emergency stop button is pressed this will disconnect CR3 allowing access to the area. whilst someone is inside power wont be able to come back on because of CR1 light sensor which will be detecting if anyone is in the area. If I'm right on how this works then i don't understand CR3 '=/'. I doubt that I am right though because this is just a bit of a guess.

If anyone could help my understand this I'd be really grateful, thanks in advance.

 

[DPG]

If you're not comfortable doing it I would sub it to someone else. Need to be 100% sure of things with these sort of safety circuits.

 

[Lucien Nunes]

I think it's a course exercise! It's normal ladder logic, you need to learn the symbols and conventions first. CR 1,2,3 are relays, their coils are the circles, the parallel vertical lines normally-open contacts, ditto with an oblique slash through normally-closed. Together, the three relays make a cross-checking arrangement for a simple start/stop setup that will not fail in a dangerous way if any one relay fails. The controlling elements are the start and stop buttons and the output is the contactor coil that seems to be labelled 'equipment'

Each 'rung' of the ladder makes a logical computation by completing a circuit from one side of the supply to the other when certain conditions are satisfied. From top to bottom, you have:

If E-stop is normal AND (CR1 operated OR CR3 operated) then CR1 coil is energised.
If E-stop is normal AND (CR2 operated OR CR3 operated) then CR2 coil is energised.
If start is pressed AND CR1 is NOT operated AND CR2 is NOT operated then CR3 coil is energised.
If CR1 is operated AND CR2 is operated AND CR3 is NOT operated, contactor 'eqmt' is energised.

Obviously the implication is that this logic is constructed not with physical relays but virtually within the PLC. I will leave it to you to work out how this configuration of four logical equations implements the fail-safe redundancy and achieves its intended control function.

You should be able to construct a sequence of operations that begins with pressing the start button, that explains the role each coil and contact plays as the sequence progresses. See my post on a two-stage starter as an example: Walk-through of starter logic
The schematic is a few posts upthread if you're up for working through it.

FWIW I often build configurations like this with actual hardware relays. Much more satisfying!

 

[Didawdidaw]

I think it's a course exercise! It's normal ladder logic, you need to learn the symbols and conventions first. CR 1,2,3 are relays, their coils are the circles, the parallel vertical lines normally-open contacts, ditto with an oblique slash through normally-closed. Together, the three relays make a cross-checking arrangement for a simple start/stop setup that will not fail in a dangerous way if any one relay fails. The controlling elements are the start and stop buttons and the output is the contactor coil that seems to be labelled 'equipment'

Each 'rung' of the ladder makes a logical computation by completing a circuit from one side of the supply to the other when certain conditions are satisfied. From top to bottom, you have:

If E-stop is normal AND (CR1 operated OR CR3 operated) then CR1 coil is energised.
If E-stop is normal AND (CR2 operated OR CR3 operated) then CR2 coil is energised.
If start is pressed AND CR1 is NOT operated AND CR2 is NOT operated then CR3 coil is energised.
If CR1 is operated AND CR2 is operated AND CR3 is NOT operated, contactor 'eqmt' is energised.

Obviously the implication is that this logic is constructed not with physical relays but virtually within the PLC. I will leave it to you to work out how this configuration of four logical equations implements the fail-safe redundancy and achieves its intended control function.

You should be able to construct a sequence of operations that begins with pressing the start button, that explains the role each coil and contact plays as the sequence progresses. See my post on a two-stage starter as an example: Walk-through of starter logic
The schematic is a few posts upthread if you're up for working through it.

FWIW I often build configurations like this with actual hardware relays. Much more satisfying!

Ah okay I get it so its only the relay system used for the robot cell as mentioned lol! I sometimes get stuff like this warped around my head my own fault for not reading it correctly and jumping to conclusions. It definitely makes a lot more sense knowing that they are all relays.

SO the EQP is presumably the robot and that can only be turned on when CR1 and CR2 are activated and CR3 is off. BY looking at the circuit the only time CR3 can be activated is when both CR1 and CR2 are off. So if you press the emergency stop this will stop all power going threw the circuit. If the emergency stop button was held down and the re-set button was pressed this would activate CR3 but nothing would happen since CR1 and 2 need to be activated to power the equipment, meaning that when the e-stop button is active no power can go to the EQP under any circumstance. when the E-stop is back in its normally open position then the Reset/start button can be activated normally. When the reset button is pressed under this circumstance this will activate CR3 making power go threw lines 1 and 2 powering CR1 and CR2.

This is now the bit I'm a bit confuse on, but I think that its right:
when the reset button is pressed when power is going to the equipment this wouldn't matter, this is because power is present in CR1 and CR2. This makes it so that power can't go threw this line meaning that CR3 cant be activated. During the activation of CR1 and CR2 power will be present in all 3 coils for a short amount of time; this wont matter because the equipment cant be activated whilst CR3 is activated.

I'm presuming that:
when the reset button is pressed or e-stop button is pressed in the bottom half of the circuit this would act the same as pressing the buttons in the top half of the circuit. The point for this to give the equipment 2 stopping and starting points.

I'm also presuming that this system could would with just either CR1 or CR2 it does't necessary need both. The reason for adding both is for a second line of defense, by adding this it makes so that CR3 and the EQP can't both be running at the same time under any circumstance. If CR2 wasn't in the circuit then some residue current may make it so power was in all coils at the same time and may run the equipment when it's not suppose to or would it blow one of the relays?

 

[Lucien Nunes]

I strongly urge you to go through in strict chronological order of starting and stopping under normal conditions, stating explicity what each coil and contact achieves at each step. Then, repeat with various abnormalities such as a relay being stuck in one position, a short-circuited contact or a broken connection. Observe what the result is on the machine operation each time. This should answer your question about the significance of the holding contactor being duplicated (CR1 and CR2).

It will help if you are consistent with terminology. There are different terms popular in different industry sectors but for example I would say that energising the coil causes a relay to operate. De-energising it causes it to release. When it operates, normally-open contacts close and complete circuits, while normally-closed ones open and break circuits.

These distinctions between an electrical command, a mechanical response, and then an electrical consequence are important when considering failure modes. A relay that has become stuck through disuse will not operate when energised. One that is free to move but has one burnt-out N/O contact will operate but not complete that particular circuit. Etc.

 

[Didawdidaw]

I strongly urge you to go through in strict chronological order of starting and stopping under normal conditions, stating explicity what each coil and contact achieves at each step. Then, repeat with various abnormalities such as a relay being stuck in one position, a short-circuited contact or a broken connection. Observe what the result is on the machine operation each time. This should answer your question about the significance of the holding contactor being duplicated (CR1 and CR2).

It will help if you are consistent with terminology. There are different terms popular in different industry sectors but for example I would say that energising the coil causes a relay to operate. De-energising it causes it to release. When it operates, normally-open contacts close and complete circuits, while normally-closed ones open and break circuits.

These distinctions between an electrical command, a mechanical response, and then an electrical consequence are important when considering failure modes. A relay that has become stuck through disuse will not operate when energised. One that is free to move but has one burnt-out N/O contact will operate but not complete that particular circuit. Etc.

Going threw it in order defiantly helps. I didn't think about relays sticking, it makes complete sense to me why this system is used now and I'm not going lie I didn't think that I'd get my head around it.

Thanks, I really appreciate your help yet again

 

[Lucien Nunes]

Glad it was helpful. Relays can be fascinating not least because you can build systems with quite complex behaviours out of relatively few parts, each of which is simple in its own right.

A century ago, there were automatic telephone exchanges based entirely on relays and selectors that, at night when there was little actual phone traffic, and without human intervention, all high-utilisation parts of the exchange would be systematically tested in rotation by automatic test systems termed routiners built out of the same types of parts as the exchange equipment itself. The routiner would take one module offline at a time, subject it to a few dozen tests where its performance would be compared to the specification, then once complete either return it to service or print out a repair docket for it that told the maintenance crew what was wrong.

Ever been in a lift...
Express DMR controller and dispatcher working

 

[Didawdidaw]

Glad it was helpful. Relays can be fascinating not least because you can build systems with quite complex behaviours out of relatively few parts, each of which is simple in its own right.

A century ago, there were automatic telephone exchanges based entirely on relays and selectors that, at night when there was little actual phone traffic, and without human intervention, all high-utilisation parts of the exchange would be systematically tested in rotation by automatic test systems termed routiners built out of the same types of parts as the exchange equipment itself. The routiner would take one module offline at a time, subject it to a few dozen tests where its performance would be compared to the specification, then once complete either return it to service or print out a repair docket for it that told the maintenance crew what was wrong.

Ever been in a lift...
Express DMR controller and dispatcher working

I didn't realize that they played such a crucial part in them sort of systems, it's fascinating how it all works! I'm currently doing a course in electrical and mechanical engineering. I work in the mechanical side of things so I though that I'd enjoy that more, but finding out how all the electrical devices and mechanisms work is proving to be far more enjoyable.

 

[Lucien Nunes]

OK, now try getting your brain around this. A commercially-built programmable computer using only relays and crossbar switches. It computes anything mathematical that can be computed, to normal scientific precision, albeit at a fraction of the speed of an equivalent electronic computer.
FACOM relay computer working

 

[Didawdidaw]

OK, now try getting your brain around this. A commercially-built programmable computer using only relays and crossbar switches. It computes anything mathematical that can be computed, to normal scientific precision, albeit at a fraction of the speed of an equivalent electronic computer.
FACOM relay computer working

That's mad, even though I watched the whole video I couldn't even contemplate how that works. Seems like you'd need ear defenders being in there all day doing scientific equations