Modifying Servos

[aus-newb]

Hi everyone

I have a Mazak M4 that I want to retrofit with a centroid controller.
I would like to use my existing servos, as they are huge in good working order and seem to have special shaft configurations. Ajaxcnc advise that I should be able to use them, but would need to chage out the resolvers to encoders and provide new servo drives. Does anyone know if this is an easy task, and what type of controllers might be required?

[Al_The_Man]

What system was on the M4, it could be Fanuc or Mitsubishi, both used similar DC motors on their early systems, which were based on the Gettys motors. Do you have specs on the motor labels and does Centroid offer analogue (+-10v) amplifier control?
Al.

[aus-newb]

Hi Al_The_Man

The Mazak has a Fanuc 5T controller complete with fanuc motors. I am not sure on the specs, as there are no real lables on the motors and no info in the Fanuc books.

The x axis motor is about has 146mm flange while z-axis is huge with 240+mm flange and about 35mm shaft. Both have currently resolvers installed on them.

Centroid do supply dc amps, but I am not sure if they are big enough.

[Al_The_Man]

I can probabally get the ball park, they should have model 2 or 5 or somesuch,I meant does Centroid have a analogue output for 3rd party drives as you might find one of the AMC largest amps will do the trick, if the original motors had tach's on them, you can probabally do without them now as modern amplifiers are run in the Torque mode with the loop closed via the encoder only.
Also, if you obtain amplifiers that need a power supply, unless you are selling them, you could cannabalise the old amplifiers for the power supply, they are parobabally three phase at present, or are you planning on running on 1ph?
Al.

[aus-newb]

Hi Al

You are right they are called something like that I will look it up at work later today.
Ajaxcnc recommended I look up the AMC amps. I was planing to run in torque mode.

But how easy is it to swap out the resolvers with an encoder?? Do you know if the Fanuc motors have appropriate facilities to mount new encoders??

I was planning to replace the old amps and power supplies, just for ease of retrofitting. I had not thought of using the existing ones, which would definately be 3 ph. Do you know if modern amplifiers will run those motors without any problrms??

Craig

[Al_The_Man]

The resolvers are usually run off of a gear wheel to increase their resolution, you will have to find a way to mount an encoder off the end of the shaft, either by solid extension and use a Renco shaft mount encoder, or use a encoder coupling to a separate style encoder and make up a mounting, either way requires some minor engineering.
The AMC amps should have no problem with these motors, going by the size of the motors, you are going to need quite the power supply for 1 phase.
Did AjaxCNC tell you what they output in the form of amplifier control signal?
Al.

[aus-newb]

Thanks for the info. I believe the motors are in the 20 - 40A range, so I intend to run them of 3ph.

I thought that the resolvers were mounted in the back of the motors do they have some sort of gear mechanisem inside of them to work?

[ Did AjaxCNC tell you what they output in the form of amplifier control signal? ]

Do you mean +/- 10 V or something else.

Craig

[Al_The_Man]

IIRC they are geared up about 10:1 because of the fact that resolvers are relatively low resolution devices compared to encoders.
Yes, 10vdc+- was what I was after or do they use other methods?
If you are running off of 3ph then I would look into seeing if the existing power supplies in the drives can be salvaged and you will also be getting the same DC level for the new amps. They usually consist of a three ph bridge into a capacitor supply if PWM, unless they are SCR control across the 3 phases then you will be out of luck.
Al.

[aus-newb]

I am sure they use +/- 10 volts for control.

Why do you suggest seeing if the existing power supplies can be salvaged? Is if for cost reasons or compatibility reasons?

I am not sure what the PWM / SRC bit means, I am no electronics expert, thats why I was hoping to replace them with of the shelf items.

Craig

[Al_The_Man]

Amplifiers can come with or without power supply, the type without can give the option of one large power supply for all three, but with the kind of sizing you have it might be prudent to go with a power supply for each, as per the originals.
The thing is that large amplifiers with built in power supplies puts the cost up quite a bit, So by using the power supply part of the existing amps, gives you a bit more flexibility in chosing amplifiers, saves money and provides voltage compatibility with the motors. If you post the part number of the present amps I may be able to tell you what type they are.
Al.

[aus-newb]

Thanks for the great info Al. I will have to make a trip into work to see what I can dig out on serial no's. I will have to get back to you in a couple of hours. I can assure you I am all for saving money on these items and it does seem pointless to waste them, as they are working just fine.

[aus-newb]

Here are some photos of my Mazak and servo drivers (I think)
It seems the motors are Gettys type 10 and 20, 15A & 30A respectively.
Would it be suitable to reuse the amps?? and how difficult would it be to rewire those to new drivers?