Posts from — January 2016
I’ve setup a factoryswblog account on Instagram.
My primary goal is still to provide unique, longer form content; I’m still not interested in participating in real time online arguments (been there, done that, too old for that now).
However, creating new posts typically takes a lot of time, so my plan is for the Instagram account to provide more frequent updates.Â It’ll probably be more biased towards my personal interests such as pens, but I will try to include a mix of topics.
Companion Site Summary
I now have four companion sites.Â I am still figuring out what works best in what format.Â Also, by the summer I hope to revise this blog’s look a bit – I think it’s a little too busy, and I want to add an Instagram widget.Â The sites are:
- The trac wiki and repository viewer.Â I’m using it for directories, reference information, and repository viewer.Â Sometime not very soon, I will look at moving it to Redmine, since trac’s development has been pretty slow (and in my experience, it’s a pain to upgrade).
- The subversion repository.Â It holds my PCB design files and source code.Â I may eventually move it to git.
- My Youtube channel for videos.Â It currently only has 1 video, but I have a few more planned.Â Note that if your workplace has blocked Youtube, let me know.Â If blocking Youtube is a significant problem, I’ll look for alternatives.
- Finally, of course, my brand new Instagram account for more frequent updates with photos and a bit of text.
January 30, 2016 No Comments
In the Beginning: Cleanroom Conveyors
In the past few years, I’ve only worked on small systems.Â But in the early days of my automation career, over 15 years ago, I was involved in a clean room conveyor system that read, labelled, and sorted disk cassettes.Â Since I was a young pup in those days, I had absolutely no input on electrical or mechanical component selection.
The system featured a conveyor with various gates, pushers, barcode readers, labelers, photo sensors, an Omron PLC, and a PC to control everything.Â All the I/O was hardwired to the PLC.Â Since it was in a cleanroom, I got used to bunny suits – and quickly learned that if you want to type inÂ a cleanroom, you need to put on the tightestÂ gloves that won’t break.
We did get the system working reliably after various adventures such as blowing a PLC I/O module (that wasn’t me!) and reconfiguring the conveyor.
Reconfiguring the conveyor meant moving gates and sensors around. I still remember how much work it took: since all the sensors were hardwired, we had basically had to re-do the wiring when everything was changed.
So how could I wireÂ the conveyor electronics so change isn’t painful?
Two Example Situations
Let’s make up a couple ofÂ likelyÂ examples, and look at s0me possible solutions:
- We have a conveyor gate and bypass that has four photo-electric sensors and four outputs (say, to 3 pneumatic solenoids and 1 barcode reader trigger)Â that haveÂ to be moved.
- It is currently 20 feet from the PLC, and needs to be moved 10 feet down the conveyor (so it will be 30 feet away).
In all cases, the sensors and pneumatics will have to be moved;Â normally these are mounted on rails orÂ slots on the conveyor and should be easy to move.Â Â But theÂ cables can’t be movedÂ as quickly.
- Oops, we forget we needed to add 2 extra photo-electric (PE) sensors, 15 feet from the PLC.
Use HardwiredÂ Cables
If we stay with hard wired cables, there are a couple ways we could solve Scenario 1:
- Remove all the 8 20 foot cables and replaceÂ them with 8Â 30 foot cables (that’s a lot of waste and wasted work, ugh!)
- Splice 10 extra feet onto all 8Â cables to make them longer (yuck!)
- Add connectors and add another 10 footÂ extension cable to all 8 cables, or if the cables already have connectors, add another 10 footÂ extension to all 8 cables.Â This solution isn’t so horrible, except we have to do it 8 times, and connectors, while often necessary, aren’t all goodness:Â they add another potential failure point (corrosion, operator error, etc).
My memory is hazy at this point, but I’m sure we didn’t useÂ standard cables (such as M12 or M8) and thus used solution 1 or 2…
For Scenario 2, we simply run two more cables from the PLC to the input sensors.
Use Multi-Port Junction Boxes
One possibility would be to use multi-port junction boxes, available fromÂ Automation Direct, ifm, Balluff, Lumberg, Turk,Â and many others.Â These boxesÂ have standard M8 or M12 circular connectors for sensors and actuators, and then run all the signals back, over one cable, to the controller.Â The big advantage is fewer cables: a 8-input box will need only one cable, instead of eight.
I’ll assume I can get an eight port junction box that will work with 4 input and 4 outputs.Â So for Scenario 1, moving the wiring requires moving the junction box, and adding one 10 foot extension cable – a lot easier than dealing with 8 cables!
For Scenario 2, if there’s a junction box nearby with 2 spare inputs, then we can connect the PE sensors to it; otherwise we have to add a junction box at 15 feet, connect both sensors to it, and run the box’s cable back to the PLC.
Overall, using junction boxes is a big win: although it hasÂ added a some extra cost, it’s already saved us a lot in labor.Â Another plus: because the junction box just collects wires together, our PLC’s setup doesn’t have to change at all.
Use A Fieldbus (CANOpen)
Another approach is to use a fieldbus or industrial Ethernet.Â I’ll use CANOpen here, because that’s what I know best, something like theseÂ IP6xÂ productsÂ available fromÂ Schneider, Phoenix, Beckhoff, etc.Â I will assume that the CAN network uses M12 daisy-chained cables, covering the whole length of the conveyor, while each fieldbus box will have a separate M12 power cable.
So for Scenario 1, the move will require moving the CANOpen box, adding an adapter to connect the existing cables together (replace the box’s connection between cables), and adding an extra cable at the box’s newÂ location to connect to the next CANOpen box.Â The power cable to the CANOpen boxÂ will have to be extended by 10 feet (e.g. add an extension cable).
For Scenario 2, if there is a CANOpen box nearby with 2 spare inputs, then we can connect the PE sensors to it; otherwise, we have to add a CANopen box at 15 feet, add another CANOpen cable to get to the next CANOpen box, and run a power cable to the new box.
We will also have to make sure the PLC can talk to CANOpen, by using a PLC with CANOpen built-in or adding a gateway.
Compared to hard wiring, the cost is significantly more (due to the cost of the CANOpen gateway and I/O boxes), our PLC has to change (to talk to CANOpen) but changes are much easier.
Compared to using Junction Boxes, the cost is more, the PLC has to change more, but there is more flexibility (easier to add I/O, and support for more types of I/O).
Use The AS-i Fieldbus
I will assume an 4-in/4-out AS-i fieldbus box, with two flat AS-i cables (one for the network + power, the other for output power) running the length of the conveyor.
For Scenario 1, the move will require disconnecting the AS-I box from the cables, moving it to the new location, and reconnecting it.Â That’s it.Â Nothing needs to be done at the old location, because the AS-i cables are self healing, and nothing needs to be done to the AS-i cables at the new location, because the AS-i connectors are insulation piercing and can tap into the flat AS-i signal and power cable at any location.
For Scenario 2, if there is a AS-i box nearby with 2 spare inputs, then we can connect the PE sensors to it; otherwise, we simply add a new AS-i input box at the new location, attach it to the AS-i cable, and connect the PE sensors to it.
Of course, the control system will change a bit: our PLC will either need an AS-I interface module or gateway.
Overall, the cost should be roughly comparable to other fieldbuses, but significantly more than hardwiring or using junction boxes.Â However, initial installation timeÂ should be the shortest, and it’s definitely the quickest to re-configure.Â AS-i doesn’t have the flexibility to add exotic equipment such as encoders and servo motors, but it’s hard to beat for this conveyor system.
I Learned About AS-i Early On, But Too Late
I first learned about AS-i a year or two after we installed that conveyor system,Â but IÂ have always thought thatÂ the initial added expense and complications (e.g. finding a PLC that would work with AS-i) of AS-i would have been worth it in time saved, especially when making changes after installation.Â But I didn’t know about it before we started, and I didn’t get involved in specifying control systems until much later.
For our current systems, AS-i does not make sense: they are compact, do not use sensors with M8/M12 connectors, and the I/O requirements are well defined but varied.Â So I have stillÂ never used AS-i, butÂ if I ever do a conveyor or similar system again AS-i will definitely be one of the leading options.
Disclaimer: as noted, I haven’t used AS-I, junction boxes or such, but I believe my descriptions give a reasonable idea of how the different approaches would work out in practice.
January 22, 2016 No Comments
For all my few readers – and a special thank you for all the insightful comments I received this past year.
Happy New Year!
January 1, 2016 No Comments
My New Year’s resolution for blogging is obvious: catch upÂ on blogging this year.
I was fully occupied in December by trying to get some new machines shipped at work and by all the Christmas activities at home, plus some computer issues, added to all the normal stuff.
My wish list for the coming year including:
- Writing about embeddedÂ and maker topics.Â I’ve been interested in embedded systems for a long time, and I have a couple Arduino projects ready to be written up.
- Write some more pen and paper posts, with an emphasis on affordable products.Â Although I still enjoy the PenAddict.com, I’ve noticed that the average cost of the items mentioned has gone up substantially.Â So I will try to highlight affordable, yet high quality, products that I’ve found.
- Include more stories about my automation experiences.
- And, of course, I plan on continuing my automation posts, which remain the core of this blog.Â I have a number of partially finished posts, including some on AS-i and I haven’t forgotten about robots.
January 1, 2016 No Comments