New sinusoidal AC servo drive development

[lerman]

While you are at it, why not build a VFD, also?

Ken

[Xerxes]

Yes, it would be technically possible to implement a VFD in the very similar way. However I don't think there is much need for DIY VFDs since there are lots of affordable VFDs in ebay. Actually I have also done one working VFD "prototype" before this servo drive project.

[tintruder]

Xerxes,

Again, I am dumb on the total system requirements for AC Servo systems.

Whether using a unified, 3 axis board or 3 seperate single-axis boards, what other components are necessary?

Would a PC-based controller hook directly to these?

Is some sort of external power supply needed, or is it included on each driver board?

I know some stepper driver systems take multiple boxes while others are an all-in-one solution...

Basically, what does a full AC Servo CNC system for a 3-axis mill include in relation to your vision? (which I'm about ready to send you money for right now...)

Thanks,

Tom

Tom, combining many axes on single PCB gives little or no cost savings compared to single axis boards. That's why I'm going to to design a single axis drive.

[Xerxes]

They aren't dumb questions. Actually a good question.

I'm primarly developing it with opto-isolated step/dir interface that can be driven like stepper. It will also have adjustable "step multiplier" because high encoder resolution would require very high step pulse frequency. Actually my test circuit already does all that. It is also possible to implement alternative +/- 10V analog torque command input or PWM/dir input if those are needed.

Drive will require an external DC power supply. For 100Vac motors about 150Vdc would be optimal but lower voltage can be used as well. I havent decided yet if I build on-board logic voltage regulator on just add external logic voltage input (~18-24Vdc). External logic voltage option would be cheaper solution because regulating low voltage from 150Vdc is somewhat tricky.

So using drive would take:
- 50-200Vdc PSU for motors
- Possibly 18-24Vdc logic voltage supply. This solution is to be decided. Opinions?
- Possibly a simple buffer circuit to drive opto-isolated step/dir input. However I'm attempting to make inputs sensitive enough to be usable directly with PC parallel port.

[DerekZahn]

For the unit I'm building I'm requiring an 18-30v input which is then broken down to 15v and 5v for gate driving and logic purposes. Given the wide motor power voltages that are possible I couldn't figure out a good cheap way to do it on the board itself, but if you can solve that problem it would be convenient.

Lots of the Surplus Center motor users will need a 24v supply anyway to turn off the motor brake.

[FastEddie]

Im looking for a power supply I can use to test these 1000w motors as well as some of the 300w and some various steppers I have. I came across this supply Triple output bench supply . I know they would be underpowered but they should move right? Would this work? Anybody have any better ideas? Thanks

[ger21]

Im looking for a power supply I can use to test these 1000w motors as well as some of the 300w and some various steppers I have. I came across this supply Triple output bench supply . I know they would be underpowered but they should move right? Would this work? Anybody have any better ideas? Thanks

Just build a cheap 24V supply, or buy one on Ebay. That should be good enough to test them. For a lot less money.

[Xerxes]

An excellent point, DerekZahn! I almost forgot that 24Vdc brake. There is no good reason for internal logic voltage supply even when it's possible to build using switching circuits.

[DennisCNC]

^^^^Do all the AC servos have brakes in them?

[Al_The_Man]

^^^^Do all the AC servos have brakes in them?

No, its not common, it usually is a special order for applications that have overhanging loads or ballscrew back feed situations when the power is off.
Al.

[unterhaus]

The Electrocraft drives I have are very nice because they have an output that drives a relay for the brake.

[Xerxes]

I've got one more crazy power stage idea. How about taking an industrial made VFD and replacing it's logic part with custom made servo drive? It would have a ready to use output stage AND power supply.

It would call that as Ghettodrive. If there were cheap VFDs that could be modified quite easily then it might be somewhat realistic. Getting some random VFDs from ebay wouldn't work unless there are lots of exactly similar units.

Probably it's wiser to stick with the original plan

[unterhaus]

I've contemplated that idea myself. The problem is, they rarely have things segregated the way you want, it's all mixed together on one circuit board. One idea is to have use a power supply from systems that were made to be multiaxis. Kolmorgen and Electrocraft both had systems like that, but you don't find the power supplies by themselves very often.

That's why I think the IRAM_ is the best idea, almost all the high voltage stuff is built in. Now if they just built in the inrush controller, it would be great.

[Xerxes]

unterhaus, you are right about VFD construction. Utilizing it would require circuit analysis to locate the traces where PWM signals are in logic level just before the power stage. Then those traces could be cut and wires from own controller could be soldered to drive then. That's why it should be called a Ghettodrive.

IRAM_ option is still strong. There are three power variants available: 10A (IRAMS), 16A (IRAMX) and 20A (IRAMY). I haven't checked if IRAMY is pin compatible with the other two types.

[DerekZahn]

unterhaus,

how does that electrocraft drive decide when to engage the motor brake by releasing the relay?

[walter]

Thanks for doing this Xerxes! Your effort is much appreciated

Can you put my name on the list, I am definitely buying your drive. I`d like the 1kW P5 version, maybe special order or limited run, when you get the chance. Something close to 12A continuous would be great

Thanks

[waughd]

Xerxes
Maybe we all need somewhere to register our intent to buy so you can guage viability of overall project and quantities of parts required to supply demand.
Anyone have any ideas on how best to do this?
I want 3 initially, 6 eventually myself to suit 1kw P5
Des

[unterhaus]

I don't know if the electrocraft drive enables the brake when the drive is enabled, or when it is moving. Now that I think about it, it probably just passes through the enable signal. I'll see if I can test it.

[Xerxes]

waughd, I think its too early to take any "pre-orders" at this point. I will be asking to email me when the real prototype is nearly finished and it's time time to start planning group PCB orders etc.

Meanwhile here is a short video clip showing my test circuit driving 300W P5 servo. Servo is being jogged by hand by turning incremental encoder connected to step/dir input.
http://www.students.tut.fi/~kontkant/cnc/3phservo.avi
File (3MB) will be there only temporarily (=days) because I'm running out of space on this web server.

[DennisCNC]

^^You can put the video on Putfile.com