Sunday, 5 July 2020

Yaskawa Servopack SGDM-04ADA setup

Struggles with the absolute encoder:
I originally bought a 200W Servopack and a 200W motor with absolute encoder and brake. I noticed those features when I bought the motor but didn't realise I'd find it impossible to set up. Having spent wasted "several" hours trying and failing to get the Servopack to come out of baseblock, I cut my losses and gave up. I may never know what the issue was with the originals. My best guess(es) are:

  • The motor is in some way incompatible with the drive. Various of the myriad errors sort of suggested this - but it's hard to see how that could be.
  • The absolute encoder was buggered or had an incompatible signal. The data is transferred by some form of high speed (serial) comms. Possibly just RS485 or similar but I wouldn't know even if it slapped me in the face.
  • Some issue with the backup battery connection. Pretty certain this isn't the case but I get the strong impression the encoder is at the root of the issue and being an absolute encoder, it requires a battery.
  • Perhaps the drive is buggered or has too early a version of the firmware to support the motor I presented it with.
  • Fucknose. I ran out of both ideas and the will to take this any further. I have a life to live. 
Time to upgrade:
So I bit the bullet and sniffed out a matched pair that was shown to be working by the seller. While I was at it, I upgraded from a 200W system to a 400W one, as I was concerned that the drag torque on the harmonic drive was possibly going to bother the motor. The last thing I wanted was to end up having to buy a third motor and drive. The cost difference from the power upgrade was perhaps £20-25 or so. 

The absolute / braked system is now sitting on a shelf. That's how it spent most of the last decade of course, so it should be happy there....

Tuning software:
Yaskawa's SigmaWin+ software connects up via RS232 and allows complete configuration of the drive from a PC. Being Yaskawa, the servos are capable of being configured for just about anything you could imagine using a servo motor and drive for.

First look:
Firstly, let's see what it reports finding. Yep, an SGDM-04ADA Servopack and an SGMAH-04ABA21. That's a 400W Sigma II Servopack (we are now at Sigma 7, IIRC) and matching 400W motor with 16 bit (relative) encoder. That's a good start.

I could see from the ebay photos that these were no spring chickens. The Korean seller had posted YT videos of them working some years back, when they had already been removed from equipment. Sure enough, the motor has just celebrated its 20th anniversary.

Although the Servopack itself is "only" 13.5 years old. I knew this when I bought them but the data is burned into the components and can be see via the software. At least it's still talking to us.

These compts came from equipment, that was either scrapped or had a scheduled replacement of critical parts, so likely had settings according to those applications. Best for me to start all over again. For this, there is a step-by-step wizard to guide you through and set up all the critical parameters. 

Here's the user manual for the drive. And the Sigmawin+ software is here

Flash up the Parameter Wizard:
Here's the starting screen:

First, set up the type of control and the input types etc. I want position control using step / dir inputs. Having chosen position control, the default settings are pretty much what I need.

Then there's the Electronic Gear settings. As I have a reduction ratio in the timing belt drive, I need to make us of this.

This then provides a range of "mechanical structures". The "round table" structure is what I need.

First, select the ratio. In my case that's the 34t - 60t pulley reduction.

You can then select the minimum movement of the output (in my case I think this means the chuck on my 4th axis). 0.01 degrees resolution sounds a bit silly but it's the default. I may choose to reduce this to 0.1 degrees or so later but it will do for now. I can't recall how many decimal places the Centroid CNC12 displays but it may be convenient for them to concur. 

I may be ogliged to measure the final backlash for willy waving purposes, which will require a high step resolution. I can always dial it back again to something more sensible afterwards.

Then the "output pulses per rev" setting. This seems to set the required number of pulses from the Acorn to drive the motor one revolution. The "Position Control" "Calculate" option seems to match the gear ratio, presumably to avoid non integer results. I'm not absolutely 100% certain here but I'll be coming back to this later. I'll need to match this with the steps per rev settings for the 4th axis in the Acorn Wizard.

Then there's the IO settings. I've accepted the defaults here. I may choose to disable some of these, such as the POT and NOT (Positive Over Travel, Negative Over Travel) limit inputs and possibly the servo enable input. 

I'll have to think about how / if to connect any outputs back to the Acorn, such as the "on position" or "drive OK" type status signals.

That's it for now. At this point it's helpful to write the settings back to the drive. Pressing this "Write" button before hitting the "Finish" button is timely here.

Other wizards:
There's also a couple of wizards for optimising the PID settings, estimating MoI and searching for resonances etc. I have to say I couldn't get the Mechanical Analysis Wizard to do much. The motor makes a short noise which suggests it's being energised but I couldn't see or feel any movement. Doesn't seem likely that this actually achieved anything useful but I should worry about this later. once I've got the thing working with the Centroid controls. I wouldn't be surprised to find that the default settings are fine for my application, as I'm barely doing anything to challenge its capabilities here.

Looks impressive at first glance, although it doesn't loom like a convincing Bode plot to my eyes. Clearly I didn't achieve anything remotely useful here, so I discarded the changes.

So there you have it. I have a servo motor and drive running in the 4th axis. And a note of the settings I made on the first pass.

Saturday, 4 July 2020

4th axis - getting it together at last

So here we go. All the parts are 100% CNC machined, no manual operations. What could possibly go wrong? Time to find out....

Quick trial with a handful of fasteners:

Looking good so far...

Well that went well. No "machine fitting" required to get the fasteners in, no filing of surfaces and opening out of holes. It does happen from time to time.

So let's start to actually assemble it for real. First fit the chuck backplate onto the harmonic drive.

Then fit the harmonic drive to the front plate.

Next, reassemble the chuck. Finally, with the various plates in place and the motor / pulleys / belt fitted. 

Runout is about 30um on the body of the chuck, which seems pretty reasonable. 

Here's the motor being jogged. Haven't checked what the jog speed it but at 3000rpm (top speed), the chuck should be spinning at 60rpm (once per second).

Next - set up the Servopack using the Yaskawa tuning software. Then see about wiring it up for real to the Centroid Acorn controller. I think this should involve some conduit, screened cable and a sensible connector, so it can be removed from the machine when required.

Sunday, 28 June 2020

Side and rear plates for 4th axis

Not the most exciting part of the build but it has to be done. I have enough material to make the side and rear plates. I'll make a top cover later, when I find (buy?) some suitable material.

First, chop up the 700 x 305mm x 9.5mm plate I've had kicking around for the last 20 years or so. The Evolution mitre saw does the trick, although it's not suited to plunge cutting into the material. Requires a slightly different technique until the slot is started....

...then you are off.

Makes an unholy mess but at least there's no grit involved, unlike with an abrasive cutoff saw.

This plate is at least 20 years old to my certain knowledge. The problem there is that the polythene(?) covering has perished and is a sod to get off. Nothing easy here. Being impermeable, there's no benefit in soaking with IPA or WD40. 

And finally we're off:


Quite a bit of stickout from the vise

Tapping M4 with the tension compression head

Side plates done

Close resemblance!

The rear plate has a hole for the control cable (conduit) as well as the hole for long stock to poke through.

The Renishaw probe was essential here.

Yes, this is a broken 3.3mm drill - on the 3rd last hole of the job. It's the closest to a cockup in the entire process, presumably due to swarf clogging within the hole. I was pecking at 5mm steps with full withdrawal - but that doesn't ensure the swarf doesn't stick, even with flood coolant. Aluminium-specific drills might possibly help but I don't have any. Still, there's enough meat to tap to a 10mm or so depth as it turns out:

Well that was exciting. But at least I can now start slapping it together.

Wednesday, 24 June 2020

Chuck fixings - more chuck body machining

Got the backplate finished (finally). Looks good but as you can see, there are some features missing. My plan was to machine holes in the front of the chuck so I can fasten it to the backplate. There is no room to fit rear bolts. Arc Euro don't sell front fitting chucks at this size.

This is a cast iron body. Being round, I need some way of holding it in the vise such as a pair of vee blocks. I don't have anything suitable but I have these soft jaws that were made and used for making something a while ago. I forget what exactly.


I need to drill through the full depth of the body, then counterbore them out to fit the screw heads. So that body is upside down. And I will do best to CNC the holes and the counterbores.

First, I need to dial in the new Chinesium tip for the Renishaw probe. This requires a sensitive DTI that has a very light spring load, so the probe doesn't move when in contact.

Then set up the body with one of the slots aligned with the Y axis. 

Set the original in the centre of the bore, on the top face:

First, spot drill the 3 holes to reduce the risk of the drill wandering, as it's a 58mm deep hole. 

Here we go...

That worked out OK

Followed by counterbore and chamfer. Then doctor the screws to the correct length and diameter. I only have 3 screws the correct length and 2 of them are button heads. A quick session in the lathe got them to the right diameter.


Done. I need to clean and reassemble the chuck but it all goes together as planned.

Next - finally get the servo motor working?

Yaskawa Servopack SGDM-04ADA setup

Struggles with the absolute encoder: I originally bought a 200W Servopack and a 200W motor with absolute encoder and brake. I noticed those...