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Forum Index : Microcontroller and PC projects : EtherCAT (Beckhoff, etc.)
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| Tinine Guru  Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Probably directed @Volhout  What is with this thing? I mean, I have been aware of it but never really got to know it. Over-priced? Over-hyped? Over-complicated? I have been studying and all I do is SMH....I would never consider using this. I have clients in deep trouble. They can't build machines because Beckhoff can't deliver. Pushing me to complete my Propeller P2 motion controller. @Volhout; is this EtherCAT just another dumb religion? I can't identify a single positive feature. It's like you can't even sneeze without the appropriate license and for this, I'm seeing numbers like $2,000  Regards, Craig |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
It looks rather neat.... The master sends a frame ("telegram") to the first node. As the frame passes through (it's not loaded): The node looks for data for its address in the frame and inserts its own response into the frame. The frame continues to pass through "on the fly" to the next node. This continues until the last node is reached. That can't detect a node after it so it bounces the complete frame back to the master. No node stores the complete frame except the master. The final returned frame contains all the responses from the nodes. It's a bit like serial SPI but done over ethernet so the distances are a lot bigger. It's all done in hardware so the only delay is in the hardware propagation. Transfers within a node are done by DMA. Basically, the whole system runs at hardware speeds. The frame is kept short and the ethernet is optimised for short frames. It's a lot cleverer than that (like the master can issue the addresses to all the slaves during boot), but that's the basics as far as I can see. Edited 2022-02-25 22:45 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
@Mick, Is this similar to token-ring networks? I would never use this architecture. You have a dead digital i/o and you have to replace a whole bank of them which also involves pulling out the wiring from all other outputs. I'd love to grab these designers and see how they'd manage laying on a dirty factory floor, flashlight between their teeth and fiddle farting with this stuff.  |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
Sounds like it. The concept seems to date back to the days of the fat coax ethernet cables with repeaters at each station. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
Not exactly, I don't think. From what I can gather the nodes are normal ethernet stations. They even use a standard ethernet MAC controller, nothing special. The physical topology seems to be anything you like, including combinations (although slaves are serially connected like token ring and need 2 or more ethernet ports). The data is passed between them as a "virtual" telegram. It doesn't have the big overheads of TCP/IP or UDP/IP though, it's low level. Lots of info here. Edited 2022-02-26 01:19 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
I have done one project with Beckhoff EtherCAT (HW side). They have been chosen for that particular project (over Siemens) becuase they had safety IO modules with the fastest response time. Customer was ASML, in an application where they shoot a 40kW laser at tin droplets to turn them into plasma (where they radiate "light" with extreme short wavelength...for lithography). Anyway, when the laser beam get's out of control you have to cut it off extremely fast, or it will shoot holes in anything in it's path (0.1ms to get through a human). Another specific thing of Beckhoff is that they live/besides in a Windows environment. They use multicore processors and simply claim a core from Windows, to guarantee responsiveness of the system. You can simply code (SCADA or local HMI) applications in C++. That is all I know of it. PicomiteVGA PETSCII ROBOTS |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
It's a bit quick... From here. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
@Volhout Ah-ha! My client keeps bringing-up those "safety modules" and I really don't get it. All they do is remove power but who doesn't do that anyway? In fact, this can be a bad thing in the case of a linear axis with a lot of inertia. The out-of-control coasting can cause severe damage to the machine or injury to personnel. One of my solutions is to delay the power-removal by a few hundred ms and allow the PID to rapidly decelerate the axis (controlled), THEN remove the power. I get the distinct impression that the marketing department has repackaged something that has always existed and end-users are perceiving it as "better". Regards, Craig |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
The safety modules are just meeting safety standards (when wired correctly they detact all kinds of fault modes, i.e. wire breaks) but can be treated same as standard IO modules. So the PLC program determines what happens. If you write the PLC program to do as described above and that proves to be just as good to save human lifes (safety is always about human life, never about machine damage) ... just do it that way. There is always a shutdown procedure to follow. You can't just pull the plug on a nuclear power plant.... Volhout By the way: Beckhoff believes so much in EtherCat that their PLC modules also use it to communicate (the internal bus) internally, as well as over twisted pair and fiber connections (between systems). Edited 2022-02-26 08:44 by Volhout PicomiteVGA PETSCII ROBOTS |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
So the special thing about the safety modules is - they are inspected (like a watchdog system) for correct operation coninuously - their inputs and outputs are fault resilient and fault detecting outputs: while ON and while OFF measure the load impedance and any shorts to ground or 24V/230V Inputs: used for dual wiring/switches/logic and each connection continuously measures for shorts and opens. I think if you can convince your customer that your system is SIL6 (or whatever level of safety they aim for) it should be fine. But a single serial connection may not meet that requirement. Big thing about these safety modules is that a/ if you use them b/ if you wire them correctly You are for a large part already meeting SIL4 (or whatever level you design to) and don't have to proove you are. This all boils down to the one who gives you the order. If they have written in the order to you that some level of safety is required, it is up to you to prove it. And sometimes spending few 100 dollars on hardware for safety modules and wiring, is cheaper that the whole certification excersize. Maybe you have to invite an external specialist to do this certification (or be licensed to do it yourself). I think this is the first thing you have to do when your customer talks about safety modules: educate yourself on the safety standard(s). There are many, but most common is SIL as defined in IEC61508. And each SIL level defines the chance of human damage and failure modes. Sometimes a simple red "shutdown" button is sufficienct. Sometimes key locked gates and more are needed. wiki So in essence you calculate the chance for human damage, and all certified safety modules have manufacturer defined failure levels. When you use your P2 to fulfill a safety function you must calculate the chance for failure yourself based on - hardware failure (chip MTBF numbers may help) - software faulure - circuit failure (power supply ?) - wiring failure (single fault resilient) Edited 2022-02-26 09:13 by Volhout PicomiteVGA PETSCII ROBOTS |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
And then there's reality: H&S person: "Is there like a yellow box with flashing lights where if I stand in front of it, the machine stops?" Engineer: "Yeah" H&S: "Good, now put those earplugs back in and quit shoving those safety glasses up on your forehead!" |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
Have you *tried* sneaking past a light curtain to get to the sheet metal bender? :) Interesting stuff, Volhout. I noticed that simple nodes don't even need a cpu - they are basically a FPGA with a couple of ethernet MACs and connected to some I/O. It's a neat system. My days of IS modules, light curtains and key exchange boxes are over now. lol Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Yes, it's been a pet-peeve of mine for years. For all the "fault-tolerant, Dual-redundant safety circuitry", the operator walks away for a minute. Maintenance tech comes along, walks through the light curtain and disappears to the back of the machine. Operator returns and resumes production, to the horror of the maintenance tech. In the vast majority of cases, it's symbolic BS. |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
Yeah, education is sometimes lacking, as is a key locked mainenance switch Not BS though. Ignored, yes. Work arounds yes, sometimes even pushed from management. Production must continue. But once you lost a hand or arm, you know why this "BS" exists. PicomiteVGA PETSCII ROBOTS |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Sounds great.....until you want those nodes to work which is when the system informs you that you need to purchase the thousands of dollars worth of licenses to activate those nodes. Fortunately, it's only company money, right? |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
In fact. I was pretty excited about wireless E-stop buttons and a colleague commented "are you crazy?" No I'm not crazy....it's impossible to jumper-out a protocol but I have come across "nuisance" hard-wired E-stops that have been bypassed. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
I don't think it really matters if E-stops are wireless as long as they are continuously checked and have to respond with a "safe" message or the thing doesn't run. They also have to be securely welded in position to prevent someone from moving them. That's not easy when they are threaded onto a piece of steel pipe. :) And there are reasons why E-stop buttons are (or should be) multiple contact loops that feed safety relays and why the access gate to the rear of a press brake should be castell interlocked with the enable switch and why 11,000V switchgear has multiple interlocks and a "chicken" switch by the door so that the operator can open the main incoming feed to the sub without having to stand in front of the breaker ... All good fun. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Maybe I told this before but after 30 years in USA, I'd never even heard of a "PAT tester". Saturday morning and I believed that, as usual, I was alone in my customer's facility but as it happened, they'd scheduled this PAT guy to do his thing. I had the electrical panel doors open and my soldering iron, heat-gun etc., laying on the floor. Went to grab a coffee and returned to find this random guy sitting on my stool, testing my stuff and putting little stickers on the plugs....WTF! Me: "Are you an electrician?" Him: "No, I went on a course" Me: "Did your course teach you what would happen if your left ear comes into contact with 240v AC? Because you're about 200mm away" He left real quick. Probably went straight to the men's underwear shelf at Tesco |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
Oh, the joys of the uninitiated... Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
A bit of perspective. A bit of perspective.pdf |
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