Motion Controllers: Mixing Servos & Stepper Motors


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    Default Motion Controllers: Mixing Servos & Stepper Motors

    I'd like some educated opinions on whether I am asking for the impossible (at the DIY budget price-point, anyway) as far as my motion controller requirements for a small slant-bed project. Basically going for a low-rent miniature Tormach-type slant bed, with a servo controlled spindle/4th axis suitable for light side-work (threading, keyways, slots, engraving, that sort of thing), that gets its G-code from an Ethernet line to a laptop (probably running Mach3 or 4). If not impossible, I would also appreciate any recommendations for motion controllers that seem to satisfy my machine requirements.

    The source of my confusion over which/any controller to choose; my lathe spindle is a servo drive, the axes motors are steppers. From what I understand, it is rather impractical to drive a max-4000rpm servo spindle via step & direction input, but that seems to be exactly what is needed during the slow-speed 4th axis maneuvers. Further, it seems like the go-to options --such as SmoothStepper-- are only good for step/dir outputs. My servo-driver is an analog Baldor unit, which can only take step/dir (position control) or -/+10V analog (torque/velocity control). Is it reasonable of me to seek an "all in one" motion controller that can output the desired step/dir outputs to the spindle & axes, but is also able to control the spindle via 10V analog for velocity control? Some of the controller cards out there have a 0-10V analog spindle output option (Hicon Integra), but would I be locked into choosing one or the other spindle control method, and is there a solution for getting reverse-rotation if I go the analog route? With encoder feedback, I understand you can't just flip the motor polarity via relay & expect things to not go haywire.

    Another possible 'solution' that I thought of was to leave the servo spindle in step/dir mode always, and adjust the electronic gearing parameter (set inside the servo driver) for fast operation to obtain the desired higher RPMs for most turning operations. Again, I'm not sure if this is something that is generally adjustable during a program, or must be configured manually each time (I haven't been able to figure out whether the Baldor/ABB "MINT" drive software is capable of this for sure). A sort of "electronic manual transmission" to modify the "electronic gear ratio" for each speed regime as needed.

    For reference:
    Servo Driver is a Baldor Microflex 9A analog unit
    Servo is a Baldor BSM80C motor with 2500-line encoder feedback
    Stepper Drivers will be Gecko or some other reputable brand
    Stepper motors will be lower-speed NEMA23s in the 400oz-in range
    I'd *like* to use a single motion controller card/unit connected to a laptop w/ Mach via an ethernet cable, that interfaces with the motor drives & feedback data as needed
    --if required for accurate Z/A axis coordination, the Z-axis stepper may end up with some kind of closed loop feedback
    --I'd *like* to keep the controller cost below $500-600$ USD unless there is some significant advantage to be had

    TCB

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    Community Moderator ger21's Avatar
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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    The only issue you may run into when using step/direction on the servo drive, is that if you use a very high pulse rate from your motion controller, you may not be able to get the minimum required pulse width for the stepper drives, which is 2us for the Geckos.
    But I would think that the electronic gearing would be fine.

    I've never used a lathe, but from what I've read, I wouldn't use Mach3 for it.

    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    I think the servo driver has the same ~200kHz limit for incoming pulses as most stepper drives, so to get up to 4000rpm I'm absolutely gonna have to go with something faster than 200pulse/rev rotation on the spindle axis. As far as the X & Z, I'm not nearly as concerned; this is a mere 4"x8" class lathe, so it's not like ramping the carriage up to hundreds of inches per minute will gain me much. At any rate, the Z has 5mm pitch screws & the X has 4mm pitch, both direct-drive, so I don't think those will be hurting for speed (either way, lathe operations generally don't require as much rapid motion as mills). Since the servo has thousands of encoder positions, I think one has to set the electronic gearing at something faster than 1:1 for practically any application, but my task is to find out if it can be done mid-program automatically (vs. having to stop a file, reconfigure the drive via Baldor's software, and start a new file, every time I need to do some detail work vs. profiling at speed)

    Because the analog vs. step/dir control uses different inputs on the driver itself, I suspect I'm "stuck" with one or the other, and changing between them is akin to a BIOS setting change that could not be done while running code. However, that's more a limitation of my driver (maybe) than the motion controllers out there, for all I know.

    TCB



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    Registered Jim Dawson's Avatar
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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    It is possible to do what you want. A Galil motion controller will run steppers in open or closed loop, and servos with an analog +/- 10v signal. For ethernet operation, the DMC-20x0, DMC-21x0, DMC-41x3, and DMC-40x0 units would be what you want. ''x'' in the part number is the number of axes. I think all of these are compatible with Mach3. Right now there are a bunch of them available on EBay, from $57 and up.

    I have a combination of servos and steppers on my mill. The Z axis is a closed loop stepper, and the 4th axis is running open loop. One of these days I'll connect the spindle to the controller, for the moment I am just using an encoder to read the spindle speed, but the spindle is not under computer control.



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    Those used Galil units do seem a lot more economical than I expected; are the proprietary ribbon connectors & breakout boards I'd need to hook my drivers to available & reasonably priced? I already had to waste a bunch of time & some money tracking down an obscure Baldor motor connector, so I'd like to avoid a repeat 'scare' if I can...

    I'm not particularly familiar with the block diagram anatomy of CNC systems, yet, but from what I've seen so far everyone (ESS, Pokeys, UCCNC, Galil, Opto 22, Vital Systems) breaks all the machine jobs into components a little differently. I like the fact that Galil offers their own stepper drivers that I'd assume are more likely to play nicely with the same-brand motion controler.

    TCB



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    A number of the units on Ebay come with breakouts and cables. New cables can be purchased from Galil, and breakouts are available from a number of vendors, but are not inexpensive. I have seen a number of used ones on Ebay, and in fact just purchased a 100 pin cable and breakout the other day for about $75.

    The Galil built in stepper drives are somewhat limited, but the on board servo drives are available up to 1.2KW. I've not seen any of these on the used market. My prefered vendor for stepper drives is Automation Direct, not cheap, but high quality and very flexible. And they play nicely with Galil products. I have never found an external servo drive that Galil would not run. I've installed them as a retrofit on up to 35 KW drives.



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    Cool; I also noticed a lot of these units come with a convenient (from a cost/space standpoint) screw-terminal wire connection panel bolted to the side in lieu of a separate breakout board. I'll pore over some schematics over the next day or so, and make sure they will work for what I need. It's good to hear that they do the +/- 10V thing, since it seems rather uncommon vs. +0-10V only. The price of these things is close to my limit (apart from the few cheap ones being bidded, it seems the ethernet models command 3-500$ for the most part) but is not untenable, especially if there aren't many other options (plus I appreciate Galil's quality)

    TCB



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    Feel free to ask any questions, I've been working with Galil products for around 20 years.



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    I'll disagree with Gerry (very politely). I use Mach3 on both my mill and my lathe - and I am very happy with both. I get excellent threading.

    The big hasslecomes when you try to run a spindle as both a 'spindle' and as a 'rotary axis'. That places rather high demands on the pulse generation and the driver. Just 'low speed spindle' is much easier.

    Cheers
    Roger



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    Quote Originally Posted by RCaffin View Post
    I'll disagree with Gerry (very politely). I use Mach3 on both my mill and my lathe - and I am very happy with both. I get excellent threading.

    The big hasslecomes when you try to run a spindle as both a 'spindle' and as a 'rotary axis'. That places rather high demands on the pulse generation and the driver. Just 'low speed spindle' is much easier.

    Cheers
    Roger
    I've also seen folks use Mach3 for both mills and lathes (granted, it seems to be way, way, way more common for the former, I assume because of the weirdo tool-changer & live tool arrangements that usually plague these projects). Honestly, my only real concern with Mach3 is that it isn't getting any more (official) development, but Mach4 is still so young it still has compatibility issues (especially considering all the cheap legacy stuff in my system)

    I'm also well aware the trouble is entirely due to my wanting to have my cake & eat it too, as far as this servo-spindle, lol. However, I see that all the 'big name' fellas like Tormach are able to pull it off, so I really just need to duplicate their work with assorted junkyard parts; simple, right? The more research I do, the more 'electronic gearing' seems to be the best solution, provided it is possible. I'd easily be able to run 4000rpm using step/dir command if I am running an entire rotation per step, and if I can get the program to change the ratio on the fly, I'd be able to seamlessly transition to 8000ppr or whatever resolution the encoder is capable of for the precision moves. While I still haven't found out whether the Baldor servo driver allows for this capability, it sure seems more feasible than switching between entirely parallel control schemes (analog vs. pulse outputs use different pins & everything on these controllers)

    Here are some of the options I've found so far (thanks again for the leads; just examining their spec sheets has helped me figure out what capabilities I need). Each of these has both step/dir or +/-10V analog control and an ethernet input option:
    -Step2Linear: converts the pulse train of common stepper motion controllers into a +/-10V torque/velocity signal (unfortunately, I don't think switching between analog & pulse is possible)
    -Baldor Nextmove E100: I'd be able to set parameters & program both servo driver & controller via Mint software, and appears to still have communication capacity with the analog driver via RS485 (or at least I'd be able to interface with both of them via the same computer output, probably a USB to RS485 adapter or something like that). There is little information beyond OEM literature out there as far as using one of these for a custom CNC build.
    -National Instruments FW-7344 board/box: fancy motion features via NI Motion software (Firewire vs. Ethernet, which is fine)
    -Parker ACR9000: interpolation & coordination of any axis/axes in every direction, but requires Windows 7 or earlier for the Parker Motion Manager
    -Parker Compumotor 6Kx (x = # axes): seems similar to the ACR9000, with fewer fancy motion features at a slightly lower price point
    -Mesa Cards: more research is needed to determine exact architecture, but I think two or three cards can be connected to allow both step and analog function (but whether they are swapable I can't say). LinuxCNC software seems like a plus for lathes, according to what I've read about it
    -Delta Tau boxes, which seem similar to the Galil systems units from what I can tell
    -The Galil units mentioned earlier already, which are far more available than other used 'industry' options (and which seem to have more information about them available online, in addition to the experience of members here like Mr. Dawson)

    Oddly, most of these seem to cost around the same $500 ballpark for the most part despite being so different from each other (barring a really good deal on one of the used all-in-one boxes), so I guess the good news is I'm not being pressured into a sub-par solution. It doesn't make the decision much easier, either. For now, I'd appreciate any experience/opinions on whether any of these is notably better or worse on the software side, since that seems to be where the true differences lie when it comes to building a system.

    I noticed that Baldor/ABB doesn't seem to have a dedicated support forum as part of their website; is there a better resource out there than the Zone that I should tap into? There's like three search results for the Nextmove controller here, lol. I feel like I need to determine 'once and for all' whether my drive really has the high/low speed flexibility I require, from someone familiar with them, before I can plunk down funds on any of these options.

    TCB



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    Never mind the driver card at this stage. Let's look at what you are really trying to achieve. I suggest the following specs for the sake of argument.
    Lathe mode: 4,000 RPM, 1 - 10 PPR
    Mill mode: 1 RPM, 1000 PPR

    Now, the problem is that you are trying to span a 4,000:1 speed range. For sure, you could get that range with a stepper motor, but you will NOT get the required power/torque for a spindle. You could try for an AC servo motor or a DC servo motor, but I challenge you to find one with the low-end stability plus torque. To the best of my (limited) knowledge, that combination does not exist. If I am wrong, someone please enlighten me!

    You could do it easily if you included an auto-change MECHANICAL gear box in the drive train, but such a thing would be a little out of the hobby price range - and possibly verging on the custom.
    You could also do it with a mechnical gear box and a couple of electric clutches. I think you can get the necessary torque ratings in the clutches. But once again, custom and $$$.

    Pity!

    Cheers
    Roger



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    Default Re: Motion Controllers: Mixing Servos & Stepper Motors

    Quote Originally Posted by barnbwt View Post

    The more research I do, the more 'electronic gearing' seems to be the best solution
    If you are using an analog signal to control the drive, then you don't need to switch between pulse and analog, depending on your motion controller. As long as the motion controller is up to the task, you can tell the spindle motor to ''jog'' at 4000 RPM (speed input as encoder pulses / second) and it will do what it's told. But on the other hand if you want to rotate the spindle 90° then you just give the motion controller the speed & acceleration and the number of encoder pulses to move and tell it to go. The motion trajectory is all handled in the motion controller. Don't confuse encoder pulses with step pulses. They are different animals and only loosely related to each other.

    The only time you should require electronic gearing is for the feed and threading. The electronic gearing would be between the spindle and the axis motors.

    -Delta Tau boxes, which seem similar to the Galil systems units from what I can tell
    Delta Tau is a direct competitor of Galil, as is G&L Galil seems to be the most popular, I think because the pricing is very competitive and they are very easy to program.

    -Mesa Cards: more research is needed to determine exact architecture, but I think two or three cards can be connected to allow both step and analog function (but whether they are swapable I can't say). LinuxCNC software seems like a plus for lathes, according to what I've read about it
    Again there should be no need to switch back & forth.

    I noticed that Baldor/ABB doesn't seem to have a dedicated support forum as part of their website; is there a better resource out there than the Zone that I should tap into? There's like three search results for the Nextmove controller here, lol. I feel like I need to determine 'once and for all' whether my drive really has the high/low speed flexibility I require, from someone familiar with them, before I can plunk down funds on any of these options.

    TCB
    If your drive accepts a +/- 10V analog signal, then it should run from from 0 to max rated rpm, in either direction, under complete control from the analog signal. The encoder feedback to the motion controller determines the position and velocity.



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Motion Controllers: Mixing Servos & Stepper Motors
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