[h3ndrix]

Hey guyz,

Been a while and things are going good. After the hot spindle topic, I got started working on getting the parts for the spindle, I was able to find ABEC 5 bearing (as per heavy recommendations) which are not super expensive. I changed some minor stuff, as HuFlungDung and others had suggested, so that should be good.

On other fronts, I got my motors, they are kinda big, but for the price I couldnt let it go...the price is so ridiculous that I had to buy them. Each one of them weights 40lb. 's (got 3) and continuos stall is 5.2 Nm (thats 736 oz.in.) and peaks at 14 Nm (1982 oz.in.)
They are about 19 inches long and 4.5 inches in diameter ( I ll post some screens tomorrow). , they are AC Brushless type with resolver but No encoder...so I would be very thankful for some encoder recommendations for these motors ( other than USDigital).

I also got a smaller Brush type DC motor for the 4 th axis, which I will mount to a rotary table, that pulls 480 oz.in. I will need a brake for that but thats for later.

I am looking into buying some galil motion control card (or some other decent quality brand) that will do most stuff and has decent amounts of I/O for M code stuff. I looked into Camsoft controller but thats kinda expensive...so any recommendations on that is greatly appreciated as well. I wish Gecko made some drivers, because these motors are 230V and that kind of voltage rated drivers from AMC are not showing up on ebay.

Oh, about the subject....can someone help me out in testing these AC Brushless servo's? They are brand new, but I just want to test them to see if they will run. Is there a way to do that without hooking it up to a driver, some simple way?

Thanks ppl,

H3ndriX

[HuFlungDung]

H3ndrix,

Congrats on those big motors. You should be able to do some real damage

I would stick with the Galil PCI card stuff, mostly because that is what I know . But, at least installation is fairly simple and you can do something with it. You can also use their older ISA cards if you have a PC with an ISA slot. The actual specs of the 17xx series ISA cards are pretty much the same as the 18xx PCI, so I don't know if there is much disadvantage to the older card, which might be found on ebay for $500 or so.

You know, you don't have to buy the Camsoft controller. The Galil card has its own motion command set. It is not gcode but there might ways around that with other inexpensive software.

The thing is, you need some kind of control system and an operator I/O panel and it needs to be integrated with proper logic to run your machine safely. Either you use a PLC based system and get someone to write the ladder logic, or learn it yourself.
OR
in a system like Camsoft, you can write your own i/o logic. The Camsoft interface allows you full control of what is going on. If there are limitations, I believe they are all due to having to run Windows on the PC. Windows does not handle I/O events with great speed. That is my opinion.

If Camsoft has an equivalent competitor in flexible retrofitting, I have not heard about it. There may be someone else out there, so don't just take my advice. Maybe this Mach2 software will handle your needs, I don't know much about that. However, I do like the safety factor of a independant motion control card (in the PC) that looks after the machine motion, somewhat independantly of what Windows is doing on your main cpu.

Perhaps Centroid would be another option. I have the notion that their system works best as a package. You would have to ask about using your own components with their software.

RE: Encoders: where are the cheap ones when you need them? You could check at Servo Systems. They sometimes have factory closeouts on certain lines and you might get a deal. I bought new from Encoder Products company.

[h3ndrix]

Thx for the reply as always HFD

Here are the pictures that I promised, the motor on the left is what I have 3 of, and the motor on the right is what I am planning on using for the rotary table:



The specs:



Thx,

H3ndriX

[glentner]

Can't you use the existing resolvers instead of adding encoders?

[HuFlungDung]

Tell us what you know about it, Glenter. I'm all ears.

I did dig up this article:

http://www.controlsciences.com/resolvers.html

Apart from finding suitable resolver-to-digital convertors and making sure you have the correct voltage available for the resolver, it may be feasible. I have no idea of what the comparative costs are, though.

[Al_The_Man]

There is no real way of testing them as far as I know without hooking up to an driver amplifier, you need the commutation, there is also a way to convert the resolver to incremental pulses, the only drawback is that the resolution is usually very low. Personally I like the Renco encoders, just because they can be fitted right on the motor shaft without coupling, but that is only possible on motors with a rear shaft available.
Al

[glentner]

Well, I only know of resolvers from a Motion training class that I recently went to, and we only touched on the topic. But from my understading (and memory) there are two coils in the "resolver portion" and magnets on the rotor. When the shaft rotates, the magnets cause a sin wave on the two coils. The coils are offset 90deg to determine direction. The ouputs from the resolver just plug into the inputs of your drive/controller and it does the rest (same as encoders). Now you may have to use a more industrial drive to accept resolver inputs as they are completely different inputs then encoders. Those motors look more like "industrial grade" motors which is probably why they have resolvers.

And again, I am by no means an expert on resolvers.

[h3ndrix]

Hey Glenter,

I just did some research too about the resolution of encoders as well and according to what most say resolvers can get pretty damn accurate (+/-2' of angle for ex.) . I dont exactly understand the logic behind how they would be hooked up to regular driver after going thru a resolver to digital convertion but I would really like to learn, like HFD, what else you know glenter

Hey Al,

Thx for the reply, I am sorry to hear that, that means I have to wait a while until I can get my hands on some drivers. I will definately give Renco a call Al.

Thx guyz,


H3ndriX

[Al_The_Man]

H3..At one time siemens and others used resolvers as feedback devices in place of encoders on their DC servo motors due to the durability and ruggedness, but they were geared up to at least 10:1 or more to get fine resolution, I believe the ones used on AC servo motors for commutation are not geared and therefore thats the reason for the low resolution.
Al

[HillBilly]

You have to put a sine frequency on the stator of the resolver, usually 2.5khz.

Then you always have output even when the resolver is standing still.

Then the controller reads the phase displacement of the two output signals.

HillBilly

[arvidb]

First I'd be interested to know what driver you are planning to use with these motors. I thought most 3-ph motor drivers were proprietary and might be difficult to get to work with motors they were not originally specified for. Are there generic 3-ph servo drivers out there?

Anyway, to test the motors:

1) Spin them at 500-1000 RPM with an external motor/drill/whatever. If they can take that for a few minutes without getting hot you can be pretty sure the windings are ok. (Make sure the motor power connections aren't shorted though!)

2) Do as above and look at the voltage between different pairs of winding connections with an oscilloscope. They should look about the same (something like a sine or a +/-sine^2 graph). You're looking mostly at the condition of the rotor magnets, I think

3) Just for fun, hook up a D cell battery to a winding. The motor should jump and hold (not very strongly but enough to make it quite difficult to turn). You can do manual trapezoidal commutation by switching the battery between different windings . Also look at the cool electric lightning when you remove the battery

Arvid

[glentner]

I believe you can run any 3ph motor with a servo drive, you just wont have any feedback, therefore you have no guarantee that the output matches the input. The driver generates a fake 3ph AC sine wave out of DC voltage using Pulse Width Modulation (PWM). This changes the frequency from 60Hz to whatever you tell it to send. That's one of the ways you can slow a motor down without reducing the voltage (and torque). I was told you could get any Baldor motor out of a catalog and drive it with a servo drive. I forget which type this is called but this is 1 of 2 types of AC motor control.
I will have to skim through a couple chapters to get the correct naming.
As for the resolver, look for a driver/controller that accepts resolver feedback instead of encoder feedback. I guess you could have both for that matter. I don't know what your budget is, but I'm sure Allen-Bradley www.ab.com has one. I think thier ULTRA1000 only has encoder feedback, but I could be mistaken. I would just look up the closest AB distributer and talk to thier motion control person. I'm familier with resolver-to-digital converters.

[Al_The_Man]

Gletner, I believe you are confusing standard 3ph induction motor drives (VFD's) with AC brushless & DC brushless servo motor drives, These type of servo motors are 3ph AC motors, but have permanant magnet rotors, which in both cases require a special amplifier to drive them, each motor type having a unique rotor feedback method in order to commutate the stator winding at the correct point of rotation. The AC sinusoidal type which H3ndrix has require a sinusoidal feedback signal derived typically from a resolver, the DC brushless on the other hand have three hall effect (or equivalent) sensors to comutate the pulsating often trapezoidal type DC.
Some DC brushless motor (Aerotech for e.g.) have an encoder disk for Position control feedback, back to the Motion controller and also have hall effect tracks for motor commutation.
Al

[arvidb]

Glentner,

As Al indicated, a 3-ph servo driver won't work without feedback. It has to know the absolute rotor position at all times, to be able to commutate the motor.

Absolute rotor position can be derived from resolver (mostly used in older servos, I think), relative encoder with some kind of index pulse or phase (common in the generation of servos before the one we've got today), or high-resolution absolute encoders (common in modern servos).

Arvid

[arvidb]

Oh, and 3-ph servo motors are also quite different from your normal 3-ph induction motor.

First, servo motors have a voltage rating that is different from "ordinary" motors. If you apply 3-ph line voltage to a 200 VAC servo motor, you will very quickly burn its windings, even though the voltage are within the range of the motor.

I have a 200W 3-ph servo motor, ratings are 200 VAC and 2 amps max. However, the winding resistance is only 2 ohms! So if I were to apply 200 VAC, about 100 amperes would flow in the windings, and as you can see this would be very bad for the motor

The high voltage is used to overcome winding inductance at higher RPMs (that is, to get the current to quickly rise to max permissible). The motor is not controlled by voltage, but by current. I.e. the driver makes sure the current in the windings are exactly as required to give the torque required to keep speed and position to set values, within the capabilities of motor and driver. Do a google search on "Field Oriented Control" to learn more.

Non-servo 3-ph motors use a Variable Frequency Drive (VFD) to run the motor at a semi-fixed speed. You can change the speed, but the response is very sluggish compared to a servo. A VFD uses V/Hz control to drive the motor: it rises the voltage as the frequency increases, again to overcome inductance and thereby keep the torque at max.

I guess you could also run a servo motor with a VFD, but be sure to set the V/Hz constant low enough to never exceed the max current of the motor. This would not give you a servo motor, however! Only a servo motor used as an ordinary motor.

Arvid

[Al_The_Man]

Originally posted by arvidb
Oh, and 3-ph servo motors are also quite different from your normal 3-ph induction motor.


I have a 200W 3-ph servo motor, ratings are 200 VAC and 2 amps max. However, the winding resistance is only 2 ohms! So if I were to apply 200 VAC, about 100 amperes would flow in the windings, and as you can see this would be very bad for the motor


I guess you could also run a servo motor with a VFD, but be sure to set the V/Hz constant low enough to never exceed the max current of the motor. This would not give you a servo motor, however! Only a servo motor used as an ordinary motor.

Arvid

Arvidb, Although I agree with alot you have mentioned but the part about the '100amps would flow' does not take into account inductive reactance or impedance which is effectively the 'AC resistance' with AC you cannot apply ohms law as it applies to DC (I=E/R). If you measue the resistance of all AC inductive devices you will find a very low resistance ( try it with one of your power supply transformers for e.g). The current on AC depends on the inductance and the frequency (= impedance) of the device.

Unfortunatley applying a VFD to a servo still has the problem of no commutation feedback. I looked into that very thing myself a while back.
Al

[arvidb]

Al,

You are correct of course, the current would be much less than 100 A. However it would still be a lot higher than the maximum current for the motor, and it would smoke the motor, after first having demagnitized its rotor magnets.

The guy I bought my motor from tested it with another similar motor, so I have the fact from a first hand source

I can't see why it would not be possible to run a Permanent Magnet 3-ph motor with a VFD? The motor would "jump start" (perhaps backwards), but once the rotor is aligned with the field generated by the VFD, should run ok. At least until you overload (stall) the motor, where an induction motor would just pull with constant torque a PM motor would vibrate back and forth

Ok, so maybe not an optimal combination, but should work

Arvid

[arvidb]

I just had a look at the Baldor homepage, and it seems their current Brushless Servo Drivers use resolver feedback as standard. Yaskawa uses the absolute encoder I wrote about earlier.

H3ndriX, any luck with running/testing the motors yet?

Arvid

[h3ndrix]

Hi,

No, I was not able to test them yet. Unfortunately I dont have a VFD or any kind of drivers that I can test them with available to me. Until then, they are very heavy paper weights

Thx,

H3ndriX

[arvidb]

Well, if they are paper weights, then at least they are very cool-looking paper weights

Arvid