Hardinge Lathe CNC Retrofit/Conversion

[glbreil]

Thanks, I have what has become an older CNC mill 1997 that was built new with a Centroid M400 control. It was my first CNC anything and I found it easy to learn and operate and the few times I have had trouble I have been able to figure out the issues and repair myself, so I definitely have been looking at that as an option.

Thanks Again Gary

[Chaz]

Yep, Centroid is nice and mature and the conversational options are good too.

[glbreil]

So after doing some research it looks like I would have to replace the axis motors to go with Centroid. They have a pretty nice system that only works with AC servos, but the encoders are on the motor.

Currently the CHNC 11 has the encoders on the ball screws and there is a belt between the motor and the ball screw.

What is your feeling about the effect on accuracy if the encoders were on the motor with a belt driving the screws?

Thanks Gary

[Muzzer]

My Tree CNC lathe had encoders on the ballscrews rather than the motor, with a toothed belt between them. I replaced the brushed DC motors with LiChaun AC servos (ie encoders within the motor) and Centroid Acorn. Works fine.

I don't see any big distinction between the 2 arrangements. You still have some backlash between the ballscrew and the table / toolpost and within the slides themselves.

The next step beyond encoders on the ballscrews or motors) would be closed loop control using linear encoders (usually glass or magnetic scales). Centroid have just released the "Hickory" and "Acornsix" controllers which build on the Acorn system by catering for encoder position feedback. That might be an option if your finances permit.
https://shopcentroidcnc.com/hickory-cnc-controller/
https://shopcentroidcnc.com/acornsix-cnc-controller/

The main difference seems to be that the Hickory uses ethercat - Acornsix is probably more appropriate for the likes of us.

[glbreil]

Thanks my only real concern is that the CHNC II is billed as a super precision lathe, not that I am doing anything super precision, but I hate to introduce any additional error if it isn't necessary. When emailing with Centroid, the recommended the Hickory system and the Leadshine EL7 AC servos. If having the encoders on the motor is an ok option, it appears to be a pretty simple retrofit solution. The only other issue to overcome is that I want to use the Fanuc AC Spindle Drive and Motor, but looking at the Centroid retrofit manual, it looks like that would work as well.

I did ask them if they have a motor that will work with the Hickory controller that has a separate encoder so it could be mounted on the screw, but I haven't heard back from them yet. There are only certain motors that will work with Hickory at this time. I am not sure what is required to get the Leadshine motors mounted in place of the Siemens DC servos yet. Still looking for a drawing of the motors.

Thanks for the thoughts, Gary

[Muzzer]

Haha my Tree is described as "ultraprecision". That just seems to mean it has good quality bearings and ballscrews (all HSK) and the bed / frame is solid cast iron but still there is no means of compensating for any backlash after the ballscrews other than rely on the quality of the parts to minimise it.

I swapped the original 4000rpm 5HP DC spindle motor and drive on the Tree for a Yaskawa VFD and 3000rpm 4kW TEFC induction motor which work nicely with the Acorn using the 0-10V analog output. My Shizuoka mill came with a nice 6000rpm Hitachi induction machine, an ancient VFD and a 2 speed gearbox. With a modern Yaskawa VFD, this works fine up to 7500rpm with the Acorn. And despite being intended for industrial use with a wide speed range, the motor has no separate cooling fan. unlike the Tree which has a little blower on the side.

[glbreil]

Another bit of a worry, is that the DC servos on the machine now are 1.3NM and Centroid recommended the Leadshine ELM2 750 watt AC servo motors to go with the Hickory control. The new motors are rated at 2.39NM so, but looking at the physical size they are tiny in comparison to the Siemens DC motors. I have never had anything with AC servos, I guess that is the norm?

Thanks Gary

[m_c]

Another bit of a worry, is that the DC servos on the machine now are 1.3NM and Centroid recommended the Leadshine ELM2 750 watt AC servo motors to go with the Hickory control. The new motors are rated at 2.39NM so, but looking at the physical size they are tiny in comparison to the Siemens DC motors. I have never had anything with AC servos, I guess that is the norm?

Thanks Gary

Not entirely normal, but some older servos were quite large things, but there were still some fairly compact ones.
I'd be more interested in how the torque/speed/inertia compares.

Inertia selection isn't an area I know much about, but I know when I asked somebody who was knowledgeable about it when looking for servos for my big mill, they advised to go for the larger 1250W servos, as despite the smaller 1000W servos having comparable performance to the original 1000W DC SEM servos, they said the larger frame size would be a better match and easier to tune.

[m_c]

In short, it's unlikely to get external encoders that will work with the Hickory.

In full, Hickory is Centroid's EtherCAT system, which means technically you should be able to use any EtherCAT drives.
However the choice of EtherCAT drives is quite limited, and most EtherCAT drives are newer designs which make use of absolute/serial output encoders, not conventional quadrature output encoders.

If you could find a suitable external encoder (Leadshine EL7's are using 23-bit encoders), although you could connect it to the servo drive instead of the motor encoder, there may be a couple issues.
First is if the drive is using the encoder to establish the servo motors rotor position, then if you move the encoder to a random position, the motor could run roughly, or just not run at all.
Second is the potential issue that the drive may not handle any additional backlash between the motor and the encoder, leading to performance issues.

If you really wanted to make use of the additional encoders, you'd have to consider something like a Dynomotion Kflop or Kogna, as they can close the loop between the drive and additional encoders.

[glbreil]

Thanks, I probably should have started a new thread, but when I asked the first question I had. I idea it would lead to so many others.

I believe I have worked out how the Hickory control will give the command for the Fanuc AC spindle drive to run and control speed.

What I can’t understand of how the drive will give feed back to the control. The Fanuc drive gets feedback from the spindle encoder, but how is the position information transmitted to the control?

The drive has a Speed Arrival output which I think must transmit the position, but I don’t see where that would be received and coordinated with the axis drives for threading and such.

Gary