Using AC Servo Motors


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Thread: Using AC Servo Motors

  1. #1
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    Default Using AC Servo Motors

    Hi All;

    A friend of mine has a Tree 320 which we plan to refurbish with Mach and new controls. We would like to replace the existing DC servo motors with AC servo motors. The old DC servos are the Gould 12.5 amp stall 90 VDC motors. We have been trying to equate the motor ratings into a Horsepower or KW rating for cross reference purposes to an AC servo motor. What we have come up with so far is that we should need 750 watt AC Servo motors and drivers. We have checked the various torque ratings and they look good.

    Can someone offer some advise on selecting suitable AC servo motors?

    Thanks
    Jim

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    Default Re: Using AC Servo Motors

    Quote Originally Posted by jknee2 View Post
    Hi All;

    A friend of mine has a Tree 320 which we plan to refurbish with Mach and new controls. We would like to replace the existing DC servo motors with AC servo motors. The old DC servos are the Gould 12.5 amp stall 90 VDC motors. We have been trying to equate the motor ratings into a Horsepower or KW rating for cross reference purposes to an AC servo motor. What we have come up with so far is that we should need 750 watt AC Servo motors and drivers. We have checked the various torque ratings and they look good.

    Can someone offer some advise on selecting suitable AC servo motors?

    Thanks
    Jim
    Hi Jim- I sort of stumbled on to your post here, and wanted to ask a couple questions. How is the retro-fit of the J320 going? I had recently restored a J320 as well, except it had already been upgraded to a Delta 10, with Baldor motors. Then I upgraded the control to a Delta 50. I saw on another post that you are using a VFD drive for the spindle. Does that mean you scrapped the aluminum gearbox housing and mechanical speed control? I wound up having to design my own D/A converter to operate the pinion drive adjustable pulley. I would much rather control the RPM through a VFD though. Do you have any pics that you could share of the mill?
    Here's a couple of mine, except now the doors are back on the cabinets.... Thanks! Bill

    Sorry about the sideways pics. I can't figure out why they get turned 90.

    Using AC Servo Motors-cameringo_20160908_135651-jpg
    Using AC Servo Motors-cameringo_20160908_135638-jpg
    Using AC Servo Motors-cameringo_20160908_135706-jpg

    Last edited by fahrphrompuken; 03-21-2017 at 10:03 AM.


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    Default Re: Using AC Servo Motors

    Bill;
    We only started this retrofit a few months ago. It was put on the back burner for a long while. I don't have any useful pictures for you but I can tell you our plans for the spindle motor. We are actually replacing the existing motor with a more standard frame motor. We managed to locate a 2 HP 1800 RPM with a brake, face flange style motor to use.

    We are keeping the original gearbox which means we will still have the low/high range speed selector handle, but we removed the v-belt drive pulley from the input shaft and the variable speed pulley setup. The new motor will be installed in basically the same location as the old one and be coupled to the gearbox input shaft with a timing belt. We will be using a 1:2 step up ratio so our maximum spindle speed will be 3600 RPM at 60 Hz. We can bump it up from there if we want using the VFD. We need to make a new mounting plate for the motor which will allow us to tension the timing belt properly. The logic for changing the motor was that if we needed to make a new mounting plate it was better to make it for a motor that could be replaced easier. The original motor would be hard to find and would most likely have to be rewound if it ever failed. As you know it is a fairly uncommon frame size.

    I considered doing something with the existing variable speed pulley setup. I believe that it was driven with a stepper motor in the original design. Just seemed to be such a wonky way to go at it and hard to interface with Mach4. Maybe your custom D/A converter was your way around these issues?

    Another possibility was to fix the variable ratio pulley in a fixed position and then use the VFD. That is possible a fairly good option but in the end we went with the timing belt. Hope we won't regret the decision as the timing belt will most likely be noisier than the V-belt.

    One way or the other the VFD is the way to go. You can also run your Mill from single phase power if that is useful to you.

    Your mill looks great, ours is a real mess, when we get the grunt work done its getting a clean up and repainting. If you are interested in seeing pics of our progress as we move forward I can certainly post a few from time to time.

    Jim



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