My system is as follows...

Mach4 which currently uses an Ethernet Smoothstepper to drive the AC Servos.
SureServo AC Servos resolving to 1 micron up to 3000mm/min using differential Step/Direction inputs.

I'm currently using Mach 4 with backlash compensation, but want to get away from that.

My machine has Newall Linear scales fitted on all three axes but I've never been able to use them. It seems crazy to have them and not to be able to take advantage of the additional accuracy they will offer. However, the only options I've seen so far are outrageously expensive, but KFLOP may just provide the answer.

So the key questions are these...

1) Can I use the 1 micron Linear scales with the KFLOP controller?
2) Will it output the necessary Step/Direction outputs?
3) Will it cope with the very high resolution at 3000mm/min, and is there enough bandwidth on the USB2 connector so service that?
4) What breakout boards do you have to enable the unit to be hooked up to my existing wiring?
5) My spindle uses an analog 0-10V output. Do you have a way of connecting that up?
6) Is there a plugin for this motion controller?

I've posted a similar set of questions to KFLOP, but I'd like to hear what people on this side of the implementation have to say about it.

Any help would be very much appreciated.

I do not believe there is a Mach 4 plugin for the KFLOP.  I don't know why they haven't made one, as they had one for Mach 3.  I really like the features of the KFLOP.  I thought it was one of the better Mach 3 controllers.

The best thing to deal with backlash is to just not have backlash.  Fixing hardware with software is always a compromise. 

The second best method for dealing with backlash is dual feedback where you have an encoder on the load and one on the motor.  The Galil motion controllers are capable of doing this.  Also, some of the newer servo drives can do this as well and it is seamless.  However, there are some limitations and conditions that apply.  Such as the load encoder can't have more resolution than the motor encoder.  On my machine, I have a Galil and motors with a resolution of 12700 counts per inch.  So if I wanted to use the dual feedback capabilities of the Galil, I would need a table/load scale with a resolution LESS than 12700 counts per inch.  Say 10240 counts per inch.  But in any case, BOTH feedback encoders need to be above 10000 counts per inch in order to have .0001" resolution.  So you have to work within those parameters or you have to change something.  For instance, you may need to increase the resolution of the motor encoder, etc... 

If I couldn't get rid of backlash with preload or new screws, I would do the new servo drive that has the dual feedback capability.  As I said, it is seamless.  Much easier than tuning an analog servo controller. 

What you do need to watch out for is trying to control a machine at one resolution and use feed back at another resolution.  In other words, the step counts is the resolution that WILL control the machine on any digital servo drive.  In later Mach builds, we do have auxiliary encoder support that can be used as feedback for the DROs and tool path and the aux encoders can have a different resolution than the step count.  However, this gives you nothing in regards to a resolution increase and will not solve any backlash issues.  Say you motor encoders are 5 micron and the table scales are 1 micron.  In that scenario, you still have a 5 micron machine. 

The ESS is certainly capable of providing auxiliary encoder feedback.

So do your research and figure out exactly what you are trying to accomplish.  Higher resolution or backlash elimination? 

Steve

Thanks for that, I'll ask them to produce a plugin and see what they say.

My backlash is very small compared to most milling machines with dovetail slides. I have precision ground leadscrews that are very large for the size of the machine, and that means I can run with +/-11microns of backlash
However, that's not very good if you're trying to machine precision items.

I have very little confidence that the software it correctly implementing the backlash compensation. If I single step back and forth between two points say 10mm apart, the display shows less than 10mm travel, which is clearly wrong. because it needs to be more than 10mm to compensate for the lost motion. Whether it gets it right when it's running in continuous mode is hard to check. Single stepping doesn't work correctly any more, it does some weird move instead of the first X/Y position, and then remains one step behind for the rest of the program. All of this really needs fixing urgently. I thought it worked fine with my previous Mach4 version, but it's definitely wrong now. whether these bugs are related is hard to tell.

My goal is to use my Linear scales because they should make a huge improvement in the accuracy and virtually eliminate any backlash issues. My whole system has 1 micron resolution. The AC Servos are 1 micron, as are the Linear scales. It's a digital setup with Step & Direction inputs to the AC Servos, so there's no analog tuning. This ought to be easy to achieve if I can only find a reasonably priced motion controller. I thought I'd found that with the KFLOP unit, but that doesn't seem to be supported.

It just seems crazy to have Linear scales and not be able to take advantage of them.

I looked at the the Galil motion controllers but they're way too expensive. They also aren't packaged very conveniently if you have four axes plus a spindle output. That pushes you into their larger unit because they use an axis for the spindle. To be honest, I wan't that keen on the attitude of their sales representative either.

So in short, I want to take advantage of my 1 micron Linear encoders to achieve the resolution that the system has the potential for. It would also take me away from what I think is a pretty questionable software backlash implementation.

I've attached a couple of pictures to give you some idea of what I'm machining.

striplar,

You might look at the Vital Systems controllers.
They can use a secondary encoder input.

Bill

Thanks for that Bill, I'll take a look.

What you described is what the compromise of software backlash compensation gives you.

So your end goal is backlash elimination.  To do that with dual feedback, you will need to go to lower than a micro resolution on you motor encoder and keep the micron scales on the load.  And go with one of the two following options:

1. Galil with analog control (requires servo drives that are capable of analog control, obviously).
2. Servo drives (and possibly new motors) that will take dual encoder feedback.

No step/dir output controller will give you dual loop control simply because that needs to happen where the PID loop is closed.  This would be your servo drives, presently, as it is not done on the ESS. 

Here is a short synopsis from Galil on the subject:
https://www.galil.com/news/dmc-programming-feedback-devices/dual-loop-mode-hints-galil-motion-controllers

Like it or not, you want big boy accuracy, so you might have to step up to the price range of a Galil.  I don't know of any other controller that will give you what you want.  Maybe the Vital Systems DSPMC?  You would have to ask them and see.  But I think that controller is deprecated now.  Otherwise, can you preload your ball screws? 

Steve

Hi,
to my knowledge KFlop does not have a Mach4 plugin.

The Mach4 controllers that can 'close the loop' are the Hicon Integra (with suitable but costly activations) and the CSMIO/A which
has a buggy Mach4 plugin. Note that both of these are analogue output. You would need analogue servo amps/servos or analogue input servo
drives with encoder rotary feedback, typically DC servos.

There is a third alternative. Most of the better AC servo manufacturers produce models of servos and drives that in addition to the rotary encoder
required to enact 'Field Oriented Control' have an additional encoder input about which you can close a position loop, with say a linear scale.

I'm using B2 series Delta servos for my new build mill. They have a 160,000cpr encoder. The later model and slightly more expensive A2 series
have a 1,280,000 cpr rotary encoder AND  a second encoder input channel for closing the position loop.

With A2 series servos you could carry on using the ESS but actually close the position about your linear scales without any additional hardware other than
the servos and drives.

https://www.fasttobuy.com/delta-750w-075kw-a2-series-servo-system-drive-motor-asda20721f-ecmac10807ps-new_p27765.html

Revise my earlier estimate. I was sure that when I bought my 750W B2 series servos/drvive/cable they were $460USD per kit and the A2 series were another $50USD each.
The link prices 750W A2 kits at $725USD, rather more than they were a year or so ago. I note also that the 750W B2 series are listed at $438USD....so they have come down
a little.

https://www.fasttobuy.com/flange-80mm-239nm-ac-motor-driver-kits-with-3m-cable-220v-075kw-cnc-servo-motor-for-cnc-router_p28084.html


Craig

What you described is what the compromise of software backlash compensation gives you.

So your end goal is backlash elimination.  To do that with dual feedback, you will need to go to lower than a micro resolution on you motor encoder and keep the micron scales on the load.  And go with one of the two following options:

1. Galil with analog control (requires servo drives that are capable of analog control, obviously).
2. Servo drives (and possibly new motors) that will take dual encoder feedback.

No step/dir output controller will give you dual loop control simply because that needs to happen where the PID loop is closed.  This would be your servo drives, presently, as it is not done on the ESS. 

Here is a short synopsis from Galil on the subject:
https://www.galil.com/news/dmc-programming-feedback-devices/dual-loop-mode-hints-galil-motion-controllers

Like it or not, you want big boy accuracy, so you might have to step up to the price range of a Galil.  I don't know of any other controller that will give you what you want.  Maybe the Vital Systems DSPMC?  You would have to ask them and see.  But I think that controller is deprecated now.  Otherwise, can you preload your ball screws? 

Steve

What I've described by way of the behaviour of the Mach4 software implementation of backlash compensation, shows a bug, not what you can get with a software solution. It's clearly not implemented correctly, at least when it's single stepping.

I think I can use an analog input for the SureServo amplifiers, so I'm pretty sure this will work with Galil

The ball leadscrews are self contained items with substantial preload built into them. The term 'backlash' isn't really what we're dealing with in CNC systems, it's just lost motion due to the inherent flexibility of all of the actuating components taking up the strain against whatever loads there are. It's impossible to improve on what I have through any mechanical means. I've been involved in the CNC industry for 35 years and been involved in machine and controller design. There are only two ways to help overcome the problem. One is to apply a load thats always on one direction so there's no load reversal on the leadscrew. This is used on some Contact Lens turning lathes. It's not appropriate for large machines though. The other is to directly measure the table position with some kind of Linear Encoder.

I'll certainly look into the DSPMC, that might do what I want.

Hi,
to my knowledge KFlop does not have a Mach4 plugin.

The Mach4 controllers that can 'close the loop' are the Hicon Integra (with suitable but costly activations) and the CSMIO/A which
has a buggy Mach4 plugin. Note that both of these are analogue output. You would need analogue servo amps/servos or analogue input servo
drives with encoder rotary feedback, typically DC servos.

There is a third alternative. Most of the better AC servo manufacturers produce models of servos and drives that in addition to the rotary encoder
required to enact 'Field Oriented Control' have an additional encoder input about which you can close a position loop, with say a linear scale.

I'm using B2 series Delta servos for my new build mill. They have a 160,000cpr encoder. The later model and slightly more expensive A2 series
have a 1,280,000 cpr rotary encoder AND  a second encoder input channel for closing the position loop.

With A2 series servos you could carry on using the ESS but actually close the position about your linear scales without any additional hardware other than
the servos and drives.

https://www.fasttobuy.com/delta-750w-075kw-a2-series-servo-system-drive-motor-asda20721f-ecmac10807ps-new_p27765.html

Revise my earlier estimate. I was sure that when I bought my 750W B2 series servos/drvive/cable they were $460USD per kit and the A2 series were another $50USD each.
The link prices 750W A2 kits at $725USD, rather more than they were a year or so ago. I note also that the 750W B2 series are listed at $438USD....so they have come down
a little.

https://www.fasttobuy.com/flange-80mm-239nm-ac-motor-driver-kits-with-3m-cable-220v-075kw-cnc-servo-motor-for-cnc-router_p28084.html


Craig

Thanks for that. Unfortunately my AC Servos don't have an additional encoder input to close the loop from an auxiliary input. They were very expensive and do a superb job though, so it's not really cost effective to change them to accommodate a deficiency in the motion controller. It's a pity that the ESS doesn't implement closed look control.

I'll take a look at those motion controllers and see what these more modern drives look like.

I suspect I'll end up designing my own system in the end. It can't be that hard to take the counts coming from the ESS and a Linear encoder and introduce additional correcting counts to the AC Servo to reduce the error using a small FPGA. We're not talking about huge errors here, just 22 counts in a complete reversal. It's an interesting little project when I'm not quite so busy.

Roger

Hi,

really cost effective to change them to accommodate a deficiency in the motion controller.

I don't regard the motion controller, in your case the ESS as deficient. The trend is with motion controllers is that they are becoming simpler
and simpler, so much so that with Ethercat, and similar distributed motion control protocols, the central motion controller disappears altogether.
Servos, or rather servo drives, are becoming ever smarter and are responsible for their own motion control.

Why do you suppose that all the leading servo manufacturers have, in their top models only, these secondary encoder channels? It's not because they
expect OEM machine builders to use deficient motion controllers.

It's a pity that the ESS doesn't implement closed look control.

Personally I'm damn glad that it does not, as the complexity and cost go through the roof. The Hicon is $1200, the CSMIO/A is 600Euro and the Galill
about $2000 for three axis. Verses an ESS for $180. You do the maths.

Thus you could buy three Delta A2 servos and drives for about the same as a Galill. When I bought my 750w B2 series a year ago, the 750W A2 series
servos were $530USD, and I'm confident I could find them still at this price if I searched around which would make three servos and drives cost competitive
with a Hicon (including the activations required for closed loop servos).

They were very expensive and do a superb job though

At the time I bought my B2 series I did not understand the advantage that the A2 series had, namely the secondary encoder channel, and so did not
consider the extra as justified. It was only later that I realized the advantage, yet I have no intention of replacing by B2's, they do a superb job
as is, just as you have found with your servos. I do not have linear scales, nor do I intend on getting them. I use 32mm diameter double-nut
C5 grade BNFN THK ballscrews and I anticipate vanishingly small flexure with either the ballscrews or the hundreds of kilos of cast iron into
which they are mounted.

If you want to close the position loop around your linear scales to accommodate lost motion then the most cost effective solution is load sensing
servo/drives such as the Delta A2 series. I have no doubt you could still sell your existing servos for a pretty penny and defray at least half the cost.

Craig