Looking for a +/-10V CNC servo controller - Page 1
Forum section: electronics / projects

author: LukeW
author_rank: Frequent Contributor
timestamp: March 18, 2015, 11:57:32 am
content: I'm looking for a servo motor controller (something off the shelf) for a large machine tool retrofit/repair job.The existing servo power drives, which take a +/-10V analog input, will be retained.I'd like a device which takes step/direction TTL in, A/B/I encoder inputs, and outputs the analog +/-10V control signals. The Rutex R2040 is an existing product which fits the bill well, but it's out of stock - can anyone recommend any similar device I could get?

author: H.O
author_rank: Frequent Contributor
timestamp: March 18, 2015, 01:24:31 pm
content: Hi,So you want the position loop closed in the device you're looking for (as is the case with the R2040)?Apart from the R2040 I don't know of any off the shelf product that fits that bill exactly.It's not an off the shelf product but you could use something like the PIC-Servo SC from JR Kerr and take its locked antiphase PWM output and convert it to +/-10V to drive your servo amplifiers. There's an example of that in the manual.What will provide the step and direction signals?Reason for my question is it might be possible to skip the step and direction stage and close the position loop in that part of the system or in an external motion controller. Like, if you're retrofitting the machine with LinuxCNC or Mach3 (I'm just asuming it's something like a CNC milling machine/router/lathe) then there are many alternatives available that let you run analog servo amplifiers without going thru the intermediate step/direction step.I've developed my own step/direction servo controller chip which, just like the JR Kerr one, could be "applied" in a circuit to output +/-10V but that'll be a project and not an off the shelf product.

author: LukeW
author_rank: Frequent Contributor
timestamp: March 18, 2015, 04:27:58 pm
content: The existing system actually has two separate loops - velocity signals from tachometers in the motors, which feed back into the existing Bosch servo power amps, and position encoders which feed back into the existing Heidenhain control computer.(By the way, the planned new 5x interpolator for the Heidenhain 11uApp analog encoders is here -https://github.com/lukeweston/SinusoidalEncoder)This is very similar to the machine we're working with:http://www.machineability.com/Bridgeport_series_II.htmlOn the above page he's used the following products, which would also be suitable for what I want - if they have the 5i20 mainboard in stock, or any board that can interface into their 7i33 analog servo controller.http://store.mesanet.com/index.php?route=product/product&product_id=66http://store.mesanet.com/index.php?route=product/product&product_id=74However their 5i20 board is out of stock, plus I don't think a PCI card is ideal for compatibility with most modern PC motherboards, if it needs future replacement, plus these Mesa boards are fairly expensive once you combine the analog output boards and the main motherboard. I think PCIe or USB would be better for a modern system. But I could handle PCI (or even parallel), it's just a matter of finding a spare older motherboard to do the job.You're right in that I don't specifically care about a step-direction interface - anything that can ultimately interconnect back to the PC and talk to common software such as LinuxCNC/Mach3 would be ideal.If no better options are available, the Kerr servo controller looks workable - if it is actually in stock and obtainable.I'd like to minimise the amount of bespoke electronics construction for this project and plug-and-play off the shelf components where possible, but I also don't want costs to be too high.If it ends up being essential, I've thrown together a quick schematic for a PWM input (5V TTL) to +/-10V converter, where 50%=0V. The schematic is attached, what do you think?

author: 691175002
author_rank: Regular Contributor
timestamp: March 18, 2015, 04:54:10 pm
content: I have used a KFlop in the past and am fairly certain it will do what you want. They have an add-on board with analog outputs for this scenario, and provide good servo tuning utilities.The KFlop is extremely stable but the KMotionCNC software they provide is extremely bare bones. You can use the KFlop as an output device for Mach3 if that's your thing.LinuxCNC is probably better suited for larger projects though.

author: H.O
author_rank: Frequent Contributor
timestamp: March 18, 2015, 05:01:31 pm
content: Hi,I'm not really up to speed on what's available when it comes to LinuxCNC as I use Mach3 myself (and most stuff aren't compatible with both) but I know that the Mesa hardware is pretty common for LinuxCNC. There's also a line of products from Jon Elson (Pico Systems I believe his company is called) but I don't know much about the details.For Mach3 you have a couple different options.The KFlop combined with KAnalog from Dynomotion - USB interface, will set you back ~500USD. Has Mach3 plugin and their own CNC software.The CSMIO/IP from CSLabs - Ethernet interface, 6 axis analog output. Will set you back €600 but is more of a packaged solution compared to the KFlop+KAnalog.The DSPMC/IP from Vital system. Ethernet interface, 8 channel analog + boatload of IO. Impressive hardware but it comes at a cost.Vital system also has their Motenc line which is compatible with LinuxCNC but it's PCI based which you weren't that keen on.For LinuxCNC I'd definitely avoid going thru the step/dir "stage" since it (LinuxCNC) is designed to BE a closed loop controller (which Mach3 isn't). If you decide on Mach3 then it's a matter of what type of hardware does the job best. Personally I'd avoid the step and direction "stage" if possible and I say that even though I ripped out the analog Indramat servos on my mill and replaced them with step and direction drives - but that's another story.I don't have any commercial interests in any of the above vendors and I'm sure there are others available which I've forgot or simpy don't know about ;-)

author: dekra54
author_rank: Unknown
timestamp: March 18, 2015, 06:15:42 pm
content: Have you checked the ARGON drive from GraniteDevices ?http://granitedevices.com/digital-servo-drive-argon/I use 4 of them in an CNC Machine and they are quite good

author: LukeW
author_rank: Frequent Contributor
timestamp: April 08, 2015, 04:07:19 pm
content: We ended up ordering a CSLab CSMIO - a little bit pricey but it looks like a nice quality unit, all in one module, with analog servo amp capability, and plenty of other flexible IOs.