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Author Topic: Step-Direction Servo PID Closer - Pixi revival  (Read 2377 times)

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Step-Direction Servo PID Closer - Pixi revival
« on: September 14, 2016, 11:49:03 PM »
I've been thinking about producing a step and direction "PID servo loop closer" ... a circuit that makes a servo system "look like" a stepper motor. This is would be a new version of the Skyco P100 "Pixi" board -- a small board to enable control of analog servo drives with step/direction signals by closing the PID loop. Skyco had a good run but withdrew the product ~10 years ago.

The principle customer is one who wants to control analog servo dives with step and direction software (like Mach or EMC).

This product is personally appealing because it would allow me to replace the steppers on my Bridgeport with high-performance AC servo motors and drives. I have the motors and drives sitting on the shelf but there lacks an easy way to interface them with Mach3/4.

I think this could significantly open the market for high-performance AC servo retrofits -- especially when considering the surplus of AC servo drives and motors currently untapped by this group.

I'm finishing up my prototype now. This will be a professional product with proper documentation. Please respond If you are interested. Pass the thread along to anyone who might be interested. Let me know of other forums with similar or better visibly for this inquiry.

-Ted
Re: Step-Direction Servo PID Closer - Pixi revival
« Reply #1 on: September 15, 2016, 12:44:30 PM »
looking something like this...

Offline mc

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Re: Step-Direction Servo PID Closer - Pixi revival
« Reply #2 on: September 23, 2016, 03:18:08 PM »
In all honesty, I doubt there would be very much demand for such a device.

Nearly all modern drives will accept step/dir as an option.
On machines with more basic analogue drives/amplifiers, by the time you factor in the cost of two/three of these, will it be cheaper than just buying a controller that supports +/-10V?

To put it in context, a CS-Labs IP-A unit is €600, which is only €40 more expensive than the IP-S (step/dir) version.
A Dynomotion Kanalog add-on for the KFlop is $250.
But both those options are also giving you high quality cnc controller with 24V compatible IO.
Even in the LinuxCNC world, MESA provide +/-10V cards for not that much more than step/dir cards.

Thinking you can convert an industrial machine cheaper to a high standard is a false economy. You still need to factor in the cost/hassle of converting/interfacing any logic to low voltage. Admittedly on a basic machine there won't be much in the way of logic, but there is still a cost of converting it.
Re: Step-Direction Servo PID Closer - Pixi revival
« Reply #3 on: September 23, 2016, 03:34:44 PM »
I am sorta worried about demand. But the pixi board sold in pretty good quantities back in the day. There are a few other products out there but not with the performance for high resolution encoders at high speed.

This is for retrofit only. A 'Glue" component that is controller agnostic -- that can open a market of high-quantity of older machines and hardware with analog drives and few other options for low-cost control upgrade.

So one Pixi-board per axis + a "parallel port" controller can control high-power AC servo drives (with analog inputs). It's compelling thing when you think about. I don't think people are used to this idea because it's never really been an option. 

Offline mc

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Re: Step-Direction Servo PID Closer - Pixi revival
« Reply #4 on: September 23, 2016, 03:39:06 PM »
Old machines with original motors generally don't have high resolution encoders, so it's not really an issue.

And just how many high-power AC servo drives exist that don't support step/dir?
Any I've looked at recently all have multiple control input options.
Re: Step-Direction Servo PID Closer - Pixi revival
« Reply #5 on: September 23, 2016, 06:05:42 PM »
Old machines with original motors generally don't have high resolution encoders, so it's not really an issue.


Not sure that's really accurate. Most encoders on AC/brushless motors I find are more than accurate (4k+ edge counts/rev). 

Just type "AC servo drive" into ebay. Lots and lots of surplus AC drives and machines exist. There are huge quantities of AC motor drives mostly unusable by communities like this one for the lack of analog control. Using surplus AC servo drives would would be the least expensive way, by far, to upgrade to servo drives from steppers. with a huge increase in performance. Vast quantities of high power drives and servos can be had for cheap because the cost barrier to making them work is out of reach for most DIY CNC enthusiast.