It's an option. If you go into General config there's a setting called Home SW safety. Tick this and it will enable limits while homing. Obviously if sharing the same switch as limits this needs to be off.Quote:
Originally Posted by cropwell
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It's an option. If you go into General config there's a setting called Home SW safety. Tick this and it will enable limits while homing. Obviously if sharing the same switch as limits this needs to be off.Quote:
Originally Posted by cropwell
And do you think you'll need more than 10 inputs and 24 outputs.? I'm also not sure if some of those Outputs on the second port can be configured as inputs in software.? Only if you plan on having an ATC will you probably need more than 10 inputs.Quote:
Originally Posted by dazp1976
Regards the Cheap BOB then yes, of course, it will make a difference. It's like having 500HP engine and fitting bald tyres.? Pointless.!
Any machines only as good as the weakest link so fitting a good card with a cheap BOB that probably can't keep up doesn't make sense to me. This whole thread proves this.
I fit good electronics, which yes cost more, but I never have any of this shit to deal with and the extra cost is made back by the fact I'm not running around fixing machines or put another way the owner doesn't have any downtime which costs money.!! . . . . You get what you pay for.!
If your going to use a cheap BOB then save your money don't buy ESS or ETH400 and use Linux CNC. You have half a chance of good machine and won't cost anything other than it's a steep learning curve.
What gobsmacked me the most was the amount of noise before I ever put mains on to the VFD. It's enabling the motors that introduces all the trouble. And the fact that the same noise is on the ground of the BOB. I thought the screening and earthing was quite reasonable but noooooo!Quote:
Originally Posted by Doddy
One thing that all this does point out is how noise-resistant it is to use NC microswitches on the limits. Under normal operation all the limit inputs have a hard-wired, all metal connection short circuit on them. This is why I've never had any of this trouble before. Ironically I did briefly consider using miniature relays to act as the 12 or 24V to 5V interface but considered it unprofessional and was in fear of being laughed at by my forum fellows. Actually it would work a treat! I doubt if the variation in triggering delay would noticeably affect the accuracy of the homing and the low-pass filtering effect would be even better than your suggested opto-couplers!
Re the 'experience', which isn't really as great as you so kindly implied: When I was a trainee at the BBC, back when Boris Johnson had a poster of Prime Minister Thatcher on his school dormitory wall, one of the trainers gave a demonstration of how there's no such thing as an earth connection at radio frequencies. This was at the Daventry short wave station which is now long gone. We went out into the antenna field and he took a coin out of his pocket and dragged it at head height down the side of a steel support post which carried one of the feeders to an antenna. This post was about 20cm or so in diameter and solidly concreted into the ground. There were distinct, bright sparks between the coin and the post!
Dean,
For a commercial machine that has to earn it's keep I'm in complete agreement with you. I'd have gone bankrupt a long time ago if I were mad enough to try and use the machine I've built as part of a business. But for me it's just a toy I have in my shed and I can't justify spending large amounts of money on it for new parts I can probably do without if I apply some time and ingenuity to the problems that arise. With the $AUD currently worth no more than about 60 US cents, prices of most other board options are way too high.
In practice this $20 BOB has done everything I need from it for several years now and the current noise problem is nothing to do with the board itself. I'm actually quite impressed that it worked so reliably before, with NC microswitches to hide the problem, and has proved quite robust as well, not complaining at all when I accidentally put 12V on one of the 5V limit inputs.
Building and modifying the machine and learning from the problems that occur is part of the fun of making it for me, it's hobby in itself, though there is an ever-increasing list of other projects on hold that are waiting for it to be working properly again.
That doesn't really suprise me - I remember when I powered up my first PWM audio amplifier - which was switching roughly the same voltage and frequency as a decent microstepping drive - and the radio in the workshop promptly went off. Holding a 'scope probe 6" above the speaker leads gave a few volts of noise in thin air, I ended up using screened speaker cable :listening_headphone:. Are the cables to your motors screened I wonder? As with the sensors when I extended my cables I cut them very short then extended with screened (2 pair) which might explain why I've not had any problems in a setup which seems somewhat similar to yours - I'm using basically the same type of sensor albeit in the M8 size. The motor cable screens I returned to the HT- pins on the drivers (always return your shit to where it's generated!) which then has a VERY SHORT ground lead down to the aluminium back plate of the enclosure which acts as a ground plane - being an RF man you'll appreciate the benefits of those.Quote:
Originally Posted by Kitwn
Voicecoil,
I thought I'd been quite careful with the wiring: the BOB is in it's own aluminium box, the outputs to the drivers are 4 core screened, the cables from the drivers to the motors are screened, the PSU for the BOB (it's the original ATX supply in the PC case that is my control box) is a separate unit from the motor PSUs, the VFD is separately mounted on the wall, the spindle power cable is proper screened cable designed for the job.
The weak point is the sensor wiring which was not all screened cable for the old microswitches and has not been totally replaced yet, but will be soon. All the grounding of every component in the control box will need to be looked at again as well. No going down to the pub this evening for me!
Simon,Quote:
Originally Posted by Cube3
Apologies for not getting back to you earlier, I got somewhat sidetracked away from the original reason for this thread.
That's a very interesting video and I especially like the improvised current transformer for investigating noise, I hadn't seen that trick before but it will be useful in future. As I've discovered the VFD is not to blame (yet!), it's enabling the motors that generates the noise I'm investigating at the moment. Once that's been quietened down I can then see if the VFD adds any problems. It wasn't an issue when I had NC microswitches for limit sensors so my fingers are crossed on that one.
Well, you've done a thorough job then, strange that you're seeing so much induced noise - unless it's induced pickup of magnetic field radiation?. It will be interesting to see what you come up with as a fix.Quote:
Originally Posted by Kitwn
Hadn't considered magnetic induction, probably not the cause at such a high frequency, but I'm willing to be proved wrong. It wouldn't be the first time!Quote:
Originally Posted by Voicecoil
I've still got some investigation I want to do. The controller is connected to the machine by screened multicore cables which have plugs on the end which fit into sockets on the machine itself. The two X axis sensors and the Z&Y sensors have one 8-way for each pair. I want to disconnect the cables and see if that makes a difference. This will help to decide if the noise is being picked up in the wiring within the machine itself where the Z and Y sensor cables run through the same drag chain as the motor wiring or whether the problem is within the controller itself. Both will be dealt with anyway but knowledge is never wasted. I'm also tempted to use the technique I learned from the video that Cube3 linked to to look at the noise on the motor cables with my laptop oscilloscope. But 6MHz???
While I wait for RS to deliver the bits required I'm doing some necessary tidying up. There isn't much room in my workshop with the machine itself pulled off the wall to get at all the wiring (note for new builders: If you have to put your machine up against a wall, do NOT put the drag chains and all the gantry wiring on the 'wall' side of the machine in order to keep it conveniently out of the way). The only place to put the trolley with the PC on is in the doorway to the rest of the shed (sorry, that should be 'studio' if my wife is listening) if I want to leave it all connected so the picture below had to be taken through the window!
Attachment 27733
The weirdest things can happen with EMC issues, at 6Mz a couple of bits of wire running parallel for a few m probably makes a half decent transformer :teapot:Quote:
Originally Posted by Kitwn
No chance of that for me either - 'coz of the virus they've been shut here for over 2 weeks :dejection:Quote:
Originally Posted by Kitwn
I get noise when my stepper motors enable. It affects my FM radio.
Now.. I have no switches and all circuits etc in a metal control box. The noise is from my estop (un-screened cable in use). :concern::confusion:
This picture shows the output coupling transformer of a Marconi BD272 AM short wave radio transmitter rated at 250KW (that's a whole Megawatt peak output). I cut my teeth on these things in the 80's. All that power is being coupled through this single turn, air spaced transformer. These are the coils for 15MHz I think, but the 6MHz ones are not much bigger. The peak voltage across the primary turn is about 40KV even though it looks remarkably like a short circuit to the uninitiated.Quote:
Originally Posted by Voicecoil
Attachment 27734
Same here. The local microbreweries are doing canned takeaways though, so I can still enjoy my favourite local brew at much less than the in-a-glass price they charge if you sit on an old wooden chair in their gravel yard getting swamped by midgies and other people's children. You have to look on the bright side!Quote:
Originally Posted by Voicecoil
Western Australia has now closed it's borders to all non-essential travellers and travelling between different regions within WA without a good reason can cost you $50,000.
Thanks for posting that - awesome bit of kit even if it looks completely illogical to the uninitiated!Quote:
Originally Posted by Kitwn
This machine is 1960's technology. Some of the later, higher power designs, have water cooled the coils. A key difficulty with those was how to clamp the plastic water pipes onto the copper coils. Metal jubilee clips glowed white hot as soon as we switched the bloody thing on and plastic clips went brittle in about a week. We ended up using waxed cotton whipping cord, similar to to an old fashioned cricket bat handle. It's surprising the skills I had to learn as a BBC Transmitter Engineer back in the days when it was still fun.Quote:
Originally Posted by Voicecoil
Bet it made instant toasties. Seriously though, was all that RF energy hazardous to workers ?Quote:
Originally Posted by Kitwn
My standrad reply is "I've spent 40 years working in high RF fields and it nev, nev, nev, never did me any harm!" On one site I worked at you couldn't turn the flourescent lights off in the transmitter building. They wouldn't strike on their own but once lit they wouldn't go out until the maintenance break . They flickered in time to the program so you could set your watch by the lights: the time pips have a very obvious pattern.
High power wireless has been around for a while now and the only known risk from such non-ionising radiation is the heating effect. VERY rare that anybody gets exposed to that kind of power, only antenna workers in practice. Contact with the conductors can give you an electric shock as well, but that isn't unique to RF.
Some people claim to have been harmed by mobile phone use. A coleague of mine had a tumour the size of a tenis ball taken out of his head some years ago and it was on the side that he had a phone clamped to for half of the day, but there's no evidence that was the cause.
Ionising radiation is the dangerous stuff but that's way above even the highest frequencies used for communications.
Going back to the original topic, Kit, you don't have any transmitter masts near you ?
Have a look at that video Cube3 posted on page 1. Ferrite rings should help you there. You can wind the cable through the ring to increase it's effect.Quote:
Originally Posted by dazp1976
Attachment 27740
Sorry, I missed this comment first time round:Quote:
Originally Posted by cropwell
Actually, yes. As far as I'm aware it's the largest wireless transmitting antenna in the southern hemisphere and is about 14Km away from the CNC machine.
It transmits VLF signals for the US Navy Submarine Fleet. I thought this could be giving your sensor LEDs a buzz. The sensors themselves generate an ac em field, but I don't know the frequency, but there might be some heterodyning.Quote:
Originally Posted by Kitwn
Just a thought, but it might have no merit.
Embarrassing but I must own up: I realised during my tests that for all these years I've left the 36V supply for my stepper motors floating. Neither rail was grounded so the whole supply was bouncing up and down by 8 Volts at several KHz. It's a miracle the machine worked at all! Any way that's now fixed and some of the bits from RS have arrived, though not the screened cable for re-wiring the sensors yet.
-
Fortunately I have access to the highly sophisticated electronics test laboratory shown below and have been able to make some very revealing, noise-free measurements on the spare cheap Chinese breakout board. Earlier reported voltage measurements were made in the presence of noise and are not reliable.
-
With an input fed to the board header rather than the screw terminals, a falling voltage must drop below 0.6V to set the output of the board. A rising voltage must go above 1.7V to reset it. This gap is the hysteresis we expect from a Scmitt trigger input chip and provides some noise immunity.
-
When using normally closed (NC) microswitches as sensors the inputs are a good solid short circuit for most of the time and only open briefly during homing. Excellent noise immunity is obtained in this configuration as proved by the fact that my machine has worked reliably for a few years!
-
Using proximity sensors presents a problem, even with opto-isolators or other electronic interfacing, since the saturated collector-emitter voltage at the output of the proximity detector or from an isolator when triggered is about 0.6V. No guarantee of reliable triggering here even without noise. The use of a potential divider circuit as described earlier is an option but I've decided to use a more direct and low-impedance option... reed relays. These will be fed by an NPN emitter-follower transistor which serves to boost the current available from the proximity sensor.
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Some will scoff no doubt, but it actually makes sense for a few reasons:
I know from past experience that a solid short circuit on the inputs works reliably, even in the presence of high noise.
Low-pass filtering is excellent and requires no additional components.
When wired as I plan to have them, with the 12V from the sensor holding the relay contacts closed as the normal state (this mimics the previously known-good NC microswitches), the circuit is proof against wiring faults as any breaks will trip the limit input.
-
Regarding positional accuracy, a key point of using proximity sensors is improved repeatability over microswitches. The reed relays I'm going to use have a specified response time of 0.5mS. Allowing for, say, 20% variation that gives a repeatability of within of 0.1mS. I can't remember exactly what my second approach speed is set at for homing in LinuxCNC but if it's even as high as 1m/min that equates to a variation of around 2 microns. Which equals nothing.
The 4 relays are $20 the lot from RS, the transistors and a wee bit of veroboard are existing stock worth much less. The whole circuit has been tested on the bench ( I have 2 relays in stock already) and works a treat. So I might just have a fully working machine again well before Mark McGowan let's me back in the pub!
Attachment 27796
No scoffing from this direction.
I'm somewhat surprised with the Vce(sat) for the opto, but if that's what you've measured then that's what it is. Personally at that stage I'd be using change-over contacts for single-switched inputs and using NC=gnd, NO=5V just to yank that signal line to one rail or the other (nothing left floating).
For the nay-sayers, what Kitwn's post is providing is belted-and-braced robust and deterministic behaviour. There's too many problems in the world to save pennies on uncertainty on our machines.
Perhaps I'm feeling humbled after a day's worth of trying to get my control box switching automatically between two machines... and making some stupid assumptions... right, where's that damned scope gone...
Not measured on a specific opto, but it is the measured output voltage of the proximity sensor when triggered. Opto outputs will vary depending on device and load current but with only 0.6V to play with I'm not chancing it. I was surprised at the low trigger voltage, but it's what I measured on the board input and the chip spec says it can be as low as 0.7V
-
This is likely to be a problem with any board that only uses 5V logic on it's inputs. I assume the more expensive boards are more sophisticated. They'd better be for the difference in price.
-
I'm happy that the 10K pull-up on the board will work OK with the single pole relays. The relay will isolate the actual board input from any noise on the wiring from the sensors and the overall noise level is going to be significantly reduced by my improvements to the wiring overall.
I'll stick with my self-centred view of having BoBs and similar with opto-isolated inputs. I've never been a fan of distributing a high speed logic input signal into the big, bad world.
Now... where to buy a replacement for a badly crimped D25-26w IDC cable (Bob2->UC300) that's given me gip for the last day, on Easter Sunday?...
Throw it in the bin I say..:joker:
I'm in complete agreement with you on that one, but the logic following it probably needs to be slightly different from the input circuit to my cheapo card. Something with a supply voltage well above 5V would be a good start.Quote:
Originally Posted by Doddy
EDIT: Been doing a bit more looking at opto-couplers and there certainly is a big range of options. The Darlington output types have a higher saturated output (up to 1V) compared to the conventional type (as low as 0.1 - 0.2V at low current) so you really must choose your device, but there are devices that would interface successfully to the cheap card. Since this application is at a guaranteed very low frequency I'm happy to let old technology do the job this time.
I promise I will do exactly that. As soon as I receive your cheque for the $400 AUD or so that I'll need to replace it with something better. Now THAT'S how you give a Yorkshireman a heart attack :hysterical:Quote:
Originally Posted by JAZZCNC
If you are prepared to use Mach3/4 then I've probably got something I could send your way.Quote:
Originally Posted by Kitwn
It's a shame they've used a 74HCT14 for the buffer on your BOB, the old (and now probably uncommon) 40106 hex Schmitt buffer was a better chip for such purposes IMHO, as the threshold voltages are more or less equispaced around 1/2 the supply voltage, something like 2.3V & 2.7V.Quote:
Originally Posted by Kitwn
PM sent.Quote:
Originally Posted by JAZZCNC
Just been perusing the HDBB2 breakout board from CNC Drive. This appears to be nothing more than an up-market version of the cheap Chinese parallel port breakout board with opto-coupled inputs and a number of improved features. The company advertise this board as suitable for use with LinuxCNC direct from an old PC's parallel port as well as with CNC Drive's own products. Since this board is a necessary add-on to the UC400ETH Ethernet controller anyway, it might make a good starting buy for a budget build with the option to upgrade at a later date.
Has anybody used one of these in this way?
https://www.benl.ebay.be/itm/HDBB2-b...-/121287188690
Looks like I can get it ok so I'm leaning towards the UC300eth-5lpt and opting for a UCSB breakout board. Get some cables and NPN-NO sensors too and use it for axis, limit & stop control- http://cncdrive.com/UCSB.html.Quote:
Originally Posted by JAZZCNC
Then I'll use my cheap board for spindle control and any relays.
What do you reckon?
Futureproofs it in case I ever get to build a 3 axis ATC or similar at a later date. (likely £3000 ish with tooling....ouch!!!! :concern: Don't tell the wife!)
I'd be comfortable with the ESS but like you say. It gives me the option of going away from Mach3.
It's a tricky decision.
That UCSB board, on paper, looks to be a pretty good BoB for the extra ports on (at least) the UC300ETH. It's pricey, though, but looks to be built like the proverbial brick-outhouse. Probably a bit of an overkill for most machines (how many layers of optical isolation do you really need?) but if you're happy with the price. I'd be thinking that if I was ever to need more than the 12 outputs (bearing in mind you'll need 8-9 for a 4-axis) then I'd relegate the axis stepper signals to a cheaper BoB on the port 2/3 on the 300 and retain the highly flexible I/O of the UCSB for other purposes on the machine.
At last!! A nice man in a white van turned up today with a box from RS containing the cable for re-wiring my new proximity sensors. I managed to get the old wiring ripped out of the drag chains and the new cables in place for the Y and Z sensors before wine 'o' clock.
Tomorrow I should have time to get the two X axis sensors wiring in place and all the soldering done to connect everything up to the control box. Sadly the two remaining miniature relays for coupling the sensors into the BOB are a separate order which is still on it's way from somewhere on planet Earth, but I should be able to test all the wiring and confirm that everything else works as expected. I already have a list of outstanding projects from Mrs W-N that are waiting for the machine to be back in action so I'm hoping the relays arrive soon!
I was just getting to the end of all the new wiring when the same nice man in the same white van turned up with another parcel from RS containing the relays. Apart from a slight problem mentioned elsewhere I now have the 4 new proximity sensors wired up with screened cables back to the controller and the relay/transistor interface into the BOB finished and tested.
Tomorrow I will tidy up the impressive mess and get everything put back together and ready for testing and alignment. Auto-squaring will need to be re-calibrated and the finished aluminium (rather than the old plywood prototype) Z axis lined up as well. Might be able to make something soon!
Kit,
If you find reed relays in the homing circuit don't give you a consistent zero point, you could try DC-DC SSR's
To be honest I'm hoping I don't have to try anything else for quite a while. I've spent too much time messing about with the machine rather than making anything with it. I'm reasonably confident that the relays will work OK. The response time (including bounce) is specified at 0.5mS. Variation in response time is going to be a lot less than that, especially as they are safe in the control box and not being vibrated and bashed about like the old microswitches were. If the dimensional errors from all the other weaknesses in this machine prove to be small enough for the relays to become significant I shall be very happy!Quote:
Originally Posted by cropwell
Well I never thought we'd end up with 8 pages of guff on this over three weeks, with an assortment of new/abandoned circuit designs and quite so much head-scratching!
Anyway the machine is now back together and appears to be working every bit as well as it did before I decided to replace the microswitches with inductive proximity sensors. The real excitement is that I can now see how well the all-aluminium Z axis behaves compared to the old plywood prototype I've been using for the last year or more.
Lockdown sending us all a bit loopy that is :rolleyes:Quote:
Originally Posted by Kitwn
Just bought a load of prox sensors myself. Might get round to fitting them in the next year maybe.
Have fun with yer machine and hope it behaves for you.
Actually the lockdown isn't making too much difference in the W-N household. Except that now we have to call it "Social Distancing" instead of "Anti-Social Distancing".:glee:Quote:
Originally Posted by dazp1976
Thanks for the good wishes, I'm looking forward to getting on with the list of projects I have outstanding. Funny how everything else seems to rely on the CNC machine as soon as you have one.
Kit