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Author Topic: Mach and VFD, modbus or pwm  (Read 1773 times)

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Offline mbele

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Mach and VFD, modbus or pwm
« on: May 06, 2014, 02:32:35 AM »
Hi,

I'm upgrading spindle on my machine with VFD controled one, I'm total noob in that area, and I would appreciate any info. I have two options, Toshiba Tosvert VF-nC3 or VF-S15 - I really dont understand the difference between these two models and will probably go with cheaper one (VF-nC3).
I want to control spindle start/stop and speed from gcode. If I could perform tapping operation it would be absolutely great (is this called semi-rigid tapping in this case?) . It would be nice if I could read current/actual speed from drive, so I know when the spindle has reached commanded speed.

VFDs can be controled via Modbus-RTU / RS-485 and vendor offers USB(serial) to RS-485 interface for that. VFD speed can be controled with PWM, and for that vendor offers gizmo for interfacing parallel port output to VFD PWM input.

If I go with PWM option, i'll have to use relay+contactor for starting/stopping spindle - that's two extra ouputs, one for PWM speed control and one for the relay, right ?
I think I can save some money if I make my own serial to RS-485 interface using AM26LS31CN line driver - providing diferential TxD/RxD signals.

What do you think is better solution for Mach?

Thanks,
Mihael
« Last Edit: May 06, 2014, 02:34:09 AM by mbele »

Offline mbele

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Re: Mach and VFD, modbus or pwm
« Reply #1 on: May 08, 2014, 03:58:15 AM »
I found all the info in "modbus" section of the forum.