Category — Machine Design
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
A couple years back we had to add a UL489 circuit breaker to one of our machines.Â I ended up choosing the Weidmuller 9926 series because it was DIN rail mount, compact (only 26mm wide for double pole), affordable, and readily available.Â The 9926 worked fine in the original machine, which had a fixed panel for the electrical components.
Then another customer required a UL489 circuit breaker in our smaller machine, where the electrical equipment is mounted in a slide-out drawer.Â I made the easy decision, and specified the 9926 series again.Â Â When the first new machine was assembled, the technician noticed that if he hit the side of the electrical drawer, the circuit breaker would trip.
So we did some moreÂ testing and verified a bit ofÂ mechanical shock would cause the 9926Â to trip to the OFF position.Â However, when the electrical drawer was retracted, it was hard to get the circuit breaker to trip, so we didn’t change the circuit breaker.Â But I still wasn’t comfortable with the possibility of shock-induced trips, so I looked at other circuit breakers.
I choose because the ABL Sursum UL series from Altech because the price was within reason, I was able to get a sample to test, and they were impervious to shock.Â The Altech L series were better than the Weidmuller 9926, but I could still get them to trip via hitting them.Â Then I had the challenge of finding space, because the DIN Rail was full, and the ABL UL series was 10mm wider than the 9926, which I solved by finding a narrower power supply.
On my last trip to Excess Solutions, they had a large selection of DIN rail circuit breakers; I couldn’t resist testing them to see how shock sensitive they were; all the ones I tested passed, including models from ABB, Eaton, and Merlin Gerin.
As a side note, I enjoy seeing the where the circuit breakers were made.Â Here, the 9926 takes the prize, because it is made in Lesotho, a country inside of South Africa, by CBi (Circuit Breakers Incorporated).Â The Eaton model was made in Spain.Â I believe (but am not 100% sure) the Altech L series in made in India.Â The ABL Sursum and ABB breakers were made in Germany.CC
Final note: the 9926 series has several pluses, including compact size and competitive price, and we haven’t heard of any problems with them in our machines in the field, but they aren’t a good choice for high vibration environments or other places where they might receive mechanical shock.
November 15, 2015 No Comments
Making cables from connectors is often an adventure; today’s tale is about crimp connectors.Â I prefer crimp connectors over solder, especially trying to solder high density connectors like HD D-Sub or MDR.Â Crimp connectors are typically very affordable, and are often less fussy than IDC connectors.
Avoiding Expensive Crimpers
However, you have to have a crimper to make a good crimp connection (duh!), and crimpers from the manufacturers can be very pricey.Â For example, a while ago we used some IMS MDrives with JST crimp connectors; the official JST hand crimper was ~$1000, so we decided to use an existing crimper (which worked OK but occasionally wasn’t good enough), and just planned on redoingÂ a significant number of crimp pins.
Sometimes crimping is impossible without the correct tool.Â I have a fewÂ cute Haydon Kerk NEMA 8 stepper motors with US Digital E4P encoders – and no encoder cables.Â The E4P uses a Molex Picoblade connector; since 100 Picoblade pins costs less than one pre-wired cable from US Digital, I decided to make my own: I bought the connector shells and 100 pins, and expected a high failure rate.
I didn’t expect a 100% failure rate – even with our smallest crimper and the help of our assembly technician, I could not get an acceptable crimp using those tiny Picoblades.Â I was defeated, but I still wasn’t going to spend my hard earned cash on a crimper that I was only going to use a couple times.
Instead, I went Excess Solutions, and looked for prewired cables with Picoblades.Â I was in luck – I found some short cables.Â Then I cut open the housing with a knife, and inserted the crimped wires into my E4P Picoblade housings.Â Success!
I have an Elmo servo drive with Molex Sherlock connectors, which look just slightly less devilish than Picoblades, and I’d like to use the same solution, but unfortunately I can’t find any distributors that stock the appropriate Molex parts (68801-4044 or 68801-4045).
Molex Micro-Fits and Mini-Fits
For Molex Micro-Fit and Mini-Fit Jr, we started with the MolexÂ 64016-0201 crimper which can affordably crimp a variety of pins including Micro-Fit, Mini-Fit, KK, and CGrid.Â However, we had aÂ noticeable failure rate, and it was a little awkward, Â so we bought the dedicated crimpers for Micro-Fit (63819-0000) and Mini-Fit Jr (63819-0900).Â These crimpers are truly wonderful; it’s easy to make a good crimp with them (especially since the crimp pin is held in the correct position and orientation), and the price is reasonable considering they are made in Sweden.
My New Crimper- Hansen Hobbies Deluxe Crimper
I decided I wanted my own crimper that could handle Mini-Fits and such, and settled on the Hansen Hobbies Deluxe Crimper.Â Some of theÂ RC guys use the one from Servo City, which is substantially cheaper, but I felt more comfortable that the Hansen model would meet my needs.Â Later, I noticed a cheaper but similar looking model on Amazon.
I’m pretty happy with Hansen crimper; it was definitely worth the money.Â So far my results are:
- It worksÂ well for Mini-Fit Jr crimp pins.
- It works well for standard DSub crimp pins.
- It can do Mini-Fit Jr pins, with some failures and extra checking
- It can do High Density DSub with some failures and extra checking
- It can do Universal Mate N Lok (UMNL)Â pins, but they’re a little large
I don’t have any plans for more crimpers now, but I have to say since I do a lot of HD DSubs, the Paladin 8029Â looks sweet.Â I also might get a ratcheting ferrule crimper some day.
Inserting the Crimped Pins
Some crimp pins can be inserted any way, for example, round pins such as Dsub, HD DSub, and UMNL.Â However, many pins such as Molex Mini-Fit Jr and Micro-Fit must be inserted in the correct orientation (top towards the tab I believe)Â — but when everything is done right, they go in with an easy but satisfying click!Â Sometimes all of the pins need a little push – for that I typically use a very small flat screwdriver.
Removing Unwanted Pins
Sometimes you screw up, and often you screw up worse trying to remove that pin you put in the wrong spot.
UMNL pins are easy to remove if you have the correct TE/AMP pin remover.
However, I consider DSub pin removers to be disposable items — it’s hard to use them more than a few times.Â Sometimes they work great, often they’re a challenge.Â Micro-Fit and Mini-Fit pin removers are similar, and if the wire breaks, it’s even harder.Â Plus the Micro-Fit/Mini-Fit pin removers are only slightly more robust than DSubs, but a lot more expensive (>$15 versus ~$5).
August 24, 2015 No Comments
If you’re one of the elite few who has followed my blog for a while, you know that I like quality pens, pencils, and paper, as well as technology such as 3D Mechanical CAD.
I’ve been working on the electrical portion of a new machine, and this week I started on the layout.Â We normally let our tech do the final layout since he does the actual wiring, but I need to make sure everything will fit, and with his help, want to get as close as possible to the final arrangement.Â (Ideally, I want to work with our mechanical engineer and techÂ to get all the DIN rail and component holes placed correctly, because it’s a lot better when these holes areÂ made by the sheet metal shop.)
I thought about trying to use 3D MCAD, but decided instead to cut sheets of vellum to match the panel size, and print life size profiles of the various components.Â (I used vellum because I can easily tape and re-tape the cutouts to it).
This approach works wellÂ because:
- I don’t have to create 3D models.Â Some manufacturers do not supply 3D models.Â Using 2D prints, I can use a PDF (by using Print View and scaling the output – thanks Adobe!), a 2D file such as DXF or DWG, or 3D (by scaling the print or creating a projection).
- It’s much quicker to move the component prints around.
- And, to be honest, I like the tactile touch of moving the paper cut-outs around and that everything is life size, not downsizedÂ on a smaller computer monitor.
Doing a full 3D model does have some advantages; working in 2D, I have to make sure I accommodate how deep the components are.Â But even in 3D, you have to add extra space for hard to model items like cables.
March 28, 2015 1 Comment
We’ve used the original Ixxat USB to CAN compact interfaces for years without any problems.Â The Ixxat is inside the machine, with its USB cable (a type A male) attached to a L-Com panel mount USB adapter (type A female to type B female), which is then connected to the external computer using a standard A to B USB cable.
Since the original USB toÂ CAN compact isÂ no longer available, we have switched to its replacement, the Ixxat USB to CAN compact V2Â — only to discover the V2 wouldn’t work!
After extensive trouble shooting, we found that the V2’s worked fine when directly plugged into a PC, but most of the time did not work when inside the machine.
There might be other solutions, but the one we found was toÂ add an USB active extension cable inside the machine between the USB panel mount adapter and the V2.
The V2 is quite similar to the original, but supports USB 2.0 high speed communications.Â It also requires a very recent device driver.
February 27, 2015 2 Comments
I’ve updated my trac page on the Electro-Craft E-3618 with a scanned datasheet with information on the E-3618, E-3622, E-3626, E-3629, and E-3633, and the BDC MINI-Series servo amplifier.Â Since I only own E-3618’s, I didn’t add a new page for the other motors.
By the way, the end of Electro-Craft catalog contains a nice little overview of servo motor theory and operation.
October 21, 2014 No Comments
I now have a Trac page to keep track of the interesting 2D mechanical CAD software I have come across.
There are at least three impressive and free AutoCAD clones available; I’ve tried all three a bit, mainly for viewing DWG files, playing with PCB outlines, andÂ modifying electrical schematics (for creating electrical schematics, I highly recommend using a dedicated program, unless most of your schematics have moved into PCB schematics).
Unlike in the 3d MCAD world, I believe there are some impressive open source 2D MCAD programs, but I haven’t found time to research them…yet.
July 14, 2014 No Comments
I’ve just created a Trac page with my directory of free, affordable, and semi-affordable 3D MCAD programs.
I’ve been wanting to create some directories for a while, so I can have a central place for information, instead of having it spread out among various blog posts.Â In the past, I’ve used WordPress pages (for Piezo Motors and Industrial Robot Resources), but I’ve decided I like using Trac better, so I will be creating my new directories on my Trac site.
As I come across new or updated information, I will update these directories.Â I use them myself, and I hope they are useful to others, too.
July 2, 2014 No Comments
I’m almost done designing a set of PCBs for one of our standard machines.Â Since our customers have different safety requirements (safety controller vs safety PLC), we have to provide several different options.Â So I’m doing something that seems a little unusual: the safety components (controller, light curtain, contactors, relays) are all wired to the main break out board.
At first glance, this seems like extra work: why wire to a connector which is then plugged into a board when you can wire direct?Â However, it will save time (and probably money), because it allows us to have a standard base machine that we can change into different configurations in a short amount of time (my guess is 30-60 minutes) by simply unplugging the safety connectors, swapping out the safety controller/PLC, and plugging the new connectors in.
Even better, I don’t have to worry about wiring mistakes, because all the wiring is on the PCB.Â (Of course, this assumes the various cables are wired correctly, but with this approach, we can wire up and test the various components in advance).
As I’ve noted, we’re using Cadsoft Eagle PCB (currently on Version 5).Â However, since Eagle is running a special (get a free upgrade to Version 7 if you buy a Version 6 upgrade before V7 comes out), we’re upgrading.Â I’ve found it hard discover Cadsoft’s upgrade pricing, so we had to call and ask.Â The Professional Version (schematic + layout + autorouter) upgrade (V5 to V6) is $549.
I like the fact the Cadsoft does not ask for an annual maintenance contract; instead, tech support is free and upgrades are free for the major version.
I was planning on getting electrical schematic software, because normally creating schematics using other tools (such as AutoCAD) is a huge waste of time, and what we had been using died a while ago.Â The software I was most interested in was Radica Software’s Electra.Â It’s not based on AutoCAD (a good thing in my opinion), it’s not limited (unlike most competitors),Â the price is reasonable, and there’s no annual maintenance fee (instead, it’s like Eagle: free support + free upgrades until the next major version).Â We don’t create that many schematics, so it’s definitely not worth it to spend a lot of money every year on schematic software.Â (Note that I haven’t had time to test Electra E6 out, but I’ve seen a number of positive comments from others).
However, with these new PCBs, I’ve moved so much of the schematic into Eagle PCB, it’s really not worth it to pay for separate schematic software.Â Instead, I’ll create DXF objects from Eagle, and use those in DraftSight (a free AutoCAD clone) to create the schematic.
I’m slowly creating some pages on my Trac site with useful links and info; here are a couple that might be relevant to this post:
June 25, 2014 No Comments
I’ve been investigating affordable, automatic creation of 3D PCBs models; what I’ve found doesn’t match up well with my needs.
I would like an easier way to create accurate models of automation PCBs, such as break out boards, which mainly use through-hole connectors (think of something like my FP-SMC-1 PCB).Â I want to use the model to verify my footprints, check that everything fits together mechanically (for example, fits into the DIN rail holder without any conflicts), and do an initial check that the board will be easy to use (enough space between connectors, etc).
I’m not interested in an approximate visualization; I want accurate an accurate model (preferably exportable in STEP format) created from manufacturer’s STEP or IGES models (which are typically available for connectors).
I took a quick glance at PCB Pool’s 3D visualization service, DesignSpark PCB, and KiCAD, and felt the reward wasn’t worth the effort of trying to get everything set up.Â Later I plan on looking into this again, but for right now, I’m back to using
Alibre Geomagic Design and having fun trying to get everything to mate.Â (As far as I can tell, DesignSpark Mechanical does not support mating, and it doesn’t export STEP files, so GD is a better path for me).
May 31, 2014 No Comments