Servo motor drive A06B

[fejlong]

Hi everyone!

Hopefully I'm in the right place to ask my question. I have these Permanent Magnet Servo Motors from work that have been chucked out. These have encoders attached to their backs that fail and they are just getting scrapped. Reckon there is absolutely nothing wrong with the motors themselves, it's just the encoders.

Motors are made by Fanuc and they are proprietary, these are driven by so called amplifiers or aka drives. The data tag on the motors say different Voltages, on some is 124V, while on others are 155V depending on size. On all of them say 200V inverter(not sure why), and the frequency is 200Hz for a maximum speed of 3000Rpm. The connection is also known, that is star, and on think this can be changed to delta.

The amplifier is quite fancy bit of kit, sometimes these fail to, their role is to supply power to the motor, get feedback from the encoder and adjust as required. These are expensive and high level engineered devices(cost thousands) and it is because they need to run the motors in two modes: spindle mode and position mode. Spindle mode means it runs the motor and nothing really matters other than exact speed. Position mode means it has to be able to turn the motor at very exact increments(sometimes 0.001 degree, hence the expensive encoders), most of the time very slowly and with a lot of torque. Also, these amplifiers measure voltage feedback on motor input wires to run them as efficiently as possible, hence the name amplifiers.

Since I already have a few of them laying around, I was thinking if these could be given a second chance by making a drive for them. I've done electronics as a hobby for a few years and I'm a cnc machinist at the moment. Once seen a brushless motor driver(ESC) and BrushLess(BL) motor in a homemade RC airplane setup that used a single hall sensor as feedback to know the position of motor. A simple pwm signal was controlling the ESC which in turn powering the motor accordingly.

I'm definitely sure it would be possible to make such a similar drive as the ESC to power these motors replacing the very expensive encoders with something cheaper maybe a hall sensor or maybe something better. I only need to run them in spindle mode anyway. I'm willing to put in the work, the hours and a small investment to make this happen, but think I would need some help from more knowledgeable people along the way.

The way I'm thinking of doing it is:
- take the domestic 240V supply, filter it, and use a bridge rectifier to turn it to DC
- feed the DC voltage into a large capacitor
- release the charge from cap to motor windings
- chop voltage at motor rated voltage, example 155V
- read hall/encoder
- not sure whats next, think the feed back needs compared to control signal
- continue with some more power, less, or negative voltage for reverse rotation? Reverse rotation would be key requirement
- loop back to reading the hall encoder.

Obviously some sort of brains would be needed for this something like a PIC micro or an atmel, maybe an arduino will do? Raspberry Pi pico? ESP32 ? ...but I have all these at home.
Power delivery will need to be with mosfets I guess.

If anyone can or would like to contribute to help out on this design it would be greatly appreciated.
Thanks!

Have a great day!

[fejlong]

I guess no one is up to the challenge