[Emc-users] UK suppliers of stepper motors and drive electronics
On 12 Feb 2008 at 18:03, [EMAIL PROTECTED] wrote: EMC can do PID just fine. It's steppers that can't. Steppers lose torque as the speed increases. There is no way around this, it's just the physics of the motor. Did someone rewrite the spec for PID? used to be a way of correcting a system or process in just the same way that an operator would, and it certainly didn't require any more torque, just a wait state. PID loop will attempt to correct for a lagging motor by requesting more effort from the motor. When did this become the *only* option PID had, more torque and overspeed? I'm not trying to be funny here but I've used a lot of these technologies in the past, and yet, when it comes to EMC I'm starting to get the impression that some things are done differently. I'm not quite sure why, I'm not even sure they are, but it is the impression I'm getting, and I hope I'm wrong. Even if the motor just loses a step or two which is detected by the scale, you can't get it to catch up - it's already at the limit of its power envelope or it wouldn't have fallen behind in the first place. So, wait state, you surely aren't telling me that EMC will simply carry on thinking it is machining a part if the coupling between a motor and leadscrew fails??? You had an incorrect assumption in your original email: that using linear scales will eliminate backlash issues. NO, it won't eliminate it, but it will eliminate it from calculations, as it gives true position, not estimated position, then add fudge tables. This isn't true at all. Backlash is an uncertainty in machine position. If you're climb milling, the cutter will tend to pull the table ahead of the motor. When conventional milling, the cutter will resist motor motion. It's not possible for the control to know which type of cutting is taking place at any given time, and it may even vary within a move, so there's no way to compensate for it. eh, it is working from a tool path with a defined depth of cut and cutter overlap from last pass, direction of beds is also knows so knowing whether you are cutting on the climb or the chip is as trivial a logic problem as it is for a human operator. Additionally, de-coupling the feedback from the motor, especially through a drive with backlash, will make the system very hard to tune. The PID integrator will wind up as the motor starts to spin to take up the backlash, but the feedback won't change until the motor is already moving. The motor will slam the table into motion, at which time the PID starts to wind up the other way. The result is - you guessed it - oscillation. This is very hard to tune out. There has been some discussion recently about using both encoders and linear scales, but there isn't any software to do that yet. I think this is the different method of machine control that Kirk is talking about. As for redundancy, since EMC takes encoder feedback, there isn't really any need for a DRO - the EMC display is actual position. Listen, I know from experience that my words have a tendency to get people's backs up, and I don't want to do this, members of this list have been extremely helpful and extremely nice. But. I'm getting an awful suspicion here, and that awful suspicion (and I dearly hope I'm wrong) is that EMC is going to suffer the same problems of many open source projects, it's crap. For example, you've got the gimp, and you've got photoshop. It isn't about whether one is free as in beer or one can be modified, it is about which one is actually productive for those who wish to edit images only, and have no interest or talent in coding. Photoshop creams the gimp. The gimp is only free if my time is worth nothing, eg editing images is a hobby, not a job of work and not competing with a job of work for my time. I'm starting to suspect that EMC is a project that started out, not to emulate the commercial equivalents, but built bit by bit to do various things on the cheap, I'm starting to suspect that EMC is not a realtime machine control system, but rather an offline (non realtime) simulator that relies on assumption (I sent signals to move X 1.01 mm, therefore I shall assume it has moved 1.01 mm) I hope this is not so and I'm wrong, because if not EMC is no use to me. Please don't do the well that's open source buddy and you can always code your own solution cos after all it is free software thing on me, I'm not actually here with my primary concern being paying as little as possible or preferably nothing for software, I'd be quite prepared to pay for EMC, and as a long lime linux user I dig open source (can't code myself but there we go) but at the end of the day when it comes to all forms of software I'm looking for a tool to do a job, and I don't mind paying for a good tool. For example, you say As for redundancy, since EMC takes encoder feedback, there isn't
[Emc-users] UK suppliers of stepper motors and drive electronics.
With the experience I have gained so far, it leads me to believe that you are making choices that may make your quest more difficult. If you are trying to have a CNC machine to make parts and spend as little as appropriate for that end, then you should consider studying other machines that are already proven to perform and copy their success. If you want to explore different methods of machine control, be prepared to spend allot more time, money and run into dead-ends. You will also need to be able to develop your own software because these days, hardware won't do anything without software. whoa there, are you telling me EMC can't do PID? shirley not.. - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] UK suppliers of stepper motors and drive electronics?
http://www.arceurotrade.co.uk/Catalogue/Stepper-Motors The 180Ncm will be big enough, and at ?18.50 at the moment ... The 3 Amp driver at ?28.95 each are a good option for driving them, so for under ?150 you have all the grunt. They will run direct off the parallel port, but a simple breakout board will be useful, and all one is missing is some DC power. 35V at a few amps does not cost a lot. Thanks to both who suggested this. I'm looking at the 220 Nm ACL571157525M steppers and the SMD093064 controller x 3. The documentation doesn't show the method of connection to a PC. The sino glass scales terminate in one RS232 per each of the three axes. So, this useful breakout board which will accept 3 x whatever connectors the SMD controllers take plus the 3x RS232, presumably a PCI job? Any hints and tips much appreciated. The PSU is no problemo. TIA - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] UK suppliers of stepper motors and drive electronics?
http://www.arceurotrade.co.uk/Catalogue/Stepper-Motors The 180Ncm will be big enough, and at ?18.50 at the moment ... The 3 Amp driver at ?28.95 each are a good option for driving them, so for under ?150 you have all the grunt. They will run direct off the parallel port, but a simple breakout board will be useful, and all one is missing is some DC power. 35V at a few amps does not cost a lot. Thanks to both who suggested this. I'm looking at the 220 Nm ACL571157525M steppers and the SMD093064 controller x 3. The documentation doesn't show the method of connection to a PC. The sino glass scales terminate in one RS232 per each of the three axes. So, this useful breakout board which will accept 3 x whatever connectors the SMD controllers take plus the 3x RS232, presumably a PCI job? Any hints and tips much appreciated. The PSU is no problemo. TIA - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] UK suppliers of stepper motors and drive electronics?
Just a quickie. Can anyone recommend a UK supplier of stepper motors and associated drive electronics? eg just add mill, and computer running EMC. Mill is a light / middleweight Pinnacle universal job, XYZ travels are 400, 180, 150 mm with quill head having separate raise / lower facility and rotation about X and Y axes too. Buying a DRO today with GS500 series glass scales (5 micron) from www.machine-dro.co.uk so will hopefully be able to use output from linear scales as direct input into EMC computer, (phase 2 of the upgrade) max rapid speed of the scales is allegedly vastly in excess of anything I could need, so don't need 740 watt steppers... X table may weigh 200 lbs and perhaps another 150 for Y table, not trying to pull high G accelerations and a rapid of 300 mm per minute would be double what I'd be happy with. On a budget of course (aren't we all) but definitely prepared to pay a little more for something not prone to glitches such as interference on power rails etc causing missed steps. Doing it this way appeals to me for two reasons. 1/ redundancy, can use linear scales with either EMC computer or standalone DRO at will. 2/ eliminates backlash and screw mapping etc, linear scales will measure actual position of tables and quill. many thanks in advance. - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] DRO input
Send Emc-users mailing list submissions to emc-users@lists.sourceforge.net To subscribe or unsubscribe via the World Wide Web, visit https://lists.sourceforge.net/lists/listinfo/emc-users or, via email, send a message with subject or body 'help' to [EMAIL PROTECTED] You can reach the person managing the list at [EMAIL PROTECTED] When replying, please edit your Subject line so it is more specific than Re: Contents of Emc-users digest... Today's Topics: 1. Re: DRO input? (John Thornton) 2. Re: Emc-users DRO input? (Kirk Wallace) 3. Re: DRO input? (Jon Elson) 4. Re: DRO Input? (Jon Elson) 5. Re: DRO Input? (Jon Elson) 6. Re: DRO Input? (Jon Elson) 7. Re: DRO input? ([EMAIL PROTECTED]) 8. Re: DRO Input? (Anders Blix) 9. Re: DRO Input? (Kirk Wallace) -- Message: 1 Date: Fri, 01 Feb 2008 06:24:24 -0600 From: John Thornton [EMAIL PROTECTED] Subject: Re: [Emc-users] DRO input? That would depend on the accuracy of your scales... .4 precision (.001mm)is not cheap... In my case mine are not nearly that accurate... I guess it depends on how much accuracy is needed and the future of the machine. EMC does have screw mapping... The cheapo (relatively) DRO I'm looking at is accurate to 0.005 mm / 0.00019 which is good enough to be getting into the realms of temperature compensation for thermal expansion of the work. I accept the comments about DROs generally not liking rapids, but it has to be said rapid is a relative term, the rapid on my mill isn't going to be that rapid. I accept the points about home made DRO with the chinese non glass scales, just not robust enough, scale reader wise, against contaminants, and just not accurate enough, for what I want. I also accept the comments about modern NC servo systems never being at rest, this is a feature that I would always program out, WAIT 100 style, in g-code, I understand the benefits of this in a cut throat commercial production environment, but again, my mill won't be operating in one, so adding a whole 0.5 seconds here and there isn't going to have any downsides and will have plenty of upsides. I also accept the comments such as those above about screw mapping, but again, this is all adding an extra layer of fudge tables, whereas the DRO is measuring ACTUAL X Y Z positions. I also have to convert my mill to NC, it is currently all manual. SO it looks like (please comment) the story so far is... a/ DRO (with pukka glass scales) is a huge boon to any manual mill. b/ A DRO could almost pay for itself in calibrating the screw etc mapping in emc, both initial set up and then monthly re-calibration, unless of course your time is valueless. c/ A DRO beats EMC as a fake dro ONLY, sans servo/steppers, see point b/ re time. d/ a DRO can enhance the functionality of EMC considerably, injecting trustworthy positioning data into EMC to re-calibrate screw etc mapping on the fly. e/ For NC then EMC is obviously the answer, since EMC is likely to be part of a DIY installation, a DRO makes making all those NC conversion parts that much easier and faster... the rule of thumb is between 50% for simple parts and 90% for complex parts, for time setting up vs actual making chips time, see point b/ re time again. f/ A DRO + EMC / NC system means redundancy, *lots* of things have to go wrong before you're knocked back to a pure manual machine. g/ So the trick here is getting that electronic feedback loop, either from the DRO or from the glass scales themselves, into EMC, lacking that electronic feedback loop, putting operator pauses into the gcode of a dual system still allows periodic operator visual checking of agreement on position. h/ lacking a DRO, the answer is to retrofit my machine with precision ballscrews and to scrape the ways etc, a prospect that will take about ten time the time of fitting a DRO and cost at least five times as much in money. i/ I guess this is going to come down to a philosophical choice, do you pursue the DRO first, or the EMC + NC first? vi vs emacs anyone? cheers - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] DRO Input?
Message: 9 Date: Thu, 31 Jan 2008 13:36:51 -0800 From: Dave Engvall [EMAIL PROTECTED] Subject: Re: [Emc-users] DRO input? Hi Dave, It all depends on what you want to do. If you just want manual position then the glass scales will do your job. However, if you ever intend to control the axes then encoders mounted on the end of the ball screws would be my choice. USdigital or Automation Direct (Koyo) encoders are reasonably priced and should do the job. With respect to you all, I know about encoders, and I know any CNC control software is going to need positional input many, many times per second. but... sticking an encoder on an axis is not measuring the position of anything except the leadscrew, it takes no account whatsoever of backlash, uneven wear or pitch errors. To a certain extent you can map out backlash and areas of wear on a leadscrew, but leadscrew pitch errors are going to be tough. The DRO is, quite differently, measuring the *actual* X Y Z position, if the DRO says you are 100.000 mm from point A then you can take it to the bank. My leadscrews are ten turns to the inch, I can compensate for backlash etc manually, second nature, and even with less than theoretically perfect accuracy I can still trust feeding a leadscrew in a few thou and know and measure that the error on that movement is very small. We appear to be confusing two things. Encoding leadscrew rotational angles and feeding this back to the human brain or CNC software, and factoring in mental or electronic fudge tables for backlash and wear, can give us fairly good accuracy of MOVEMENT. A DRO with proper glass scales gives us fairly good accuracy of POSITION. 5 times a second is *plenty* for an accurate positional measurement system to update an accurate movement system, and produce a system with true accuracy. While leadscrew encoders and a copy of emc and no stepper or servo motors will indeed give me a system that will display X Y Z co-ordinates on a screen, the accuracy of these readings is going to be just as suspect as it is sans emc and encoders, only the DRO and pukka glass scales will give true positional accuracy. As someone who couldn't code hello world (except maybe in BASIC) writing the code isn't an option, so unless emc has this facility on the roadmap then being free as in beer isn't enough. Many thanks to all, hopefully there is some more meat in this subject yet. end - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] DRO input?
Sorry, haven't RTFM, downloading as I type. I'm considering buying a Far Eastern made 3 axis DRO for my Pinnacle universal mill, DRO + 3 glass scales (to 1/5thou) and all cabling etc etc for under 400 UK Pounds. This DRO has an RS232 output. So, does EMC have the facility to take absolute X Y Z positioning data from the RS232 on the DRO, rather than the traditional method of counting leadscrew revolutions and subtracting backlash and wear? TIA GF - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
