Hi folks,
  Need to start and stop a small lathe spindle in roughly 3 second intervals. ON 3, OFF 3.
RPM will be fixed, determined by pulley combination/motor RPM and need not be variable.
1/2 HP with little more inertia than the motor itself. (maybe 1.5 x)
This will run 1.2 to 1.5 million cycles per year.

Question is what would be the best method of powering the spindle considering wear and maintenance ?

1. A servo ?     Pretty pricey but would work very well ?
2. AC Motor and VFD w/dynamic braking ?   Reliable and long lasting ?
3. Stepper and Gecko ?   Advantage/ disadvantage ?
4. AC motor w/clutch-brake ?  Wear/maintenance ? (cycles per friction disc ?)
5. Commercial sewing machine type clutch motor ? I have one of these on a small Kitamura second op lathe that works very well but not sure how long it will work between adjustments or when it will wear out.  
6. Other .....

Thanks for insight.
Russ

AC servo motor set up in Vel mode is about the only solution I see all others have enharent problems with multiple restarts and fast stops and normal wear and tear.

Over a long period the cost of the AC servo system would be MUCH cheaper than Cost/ Maint on the others

Just a thought, (;-)

That's a good point TP .. thanks.

What do you see as the major problems with the VFD approach ?
Is it all digital, nothing mechanical ?

Russ

You will end up overheating the motor windings from the constant starting loads without enough time to cool them back down before the next cycle. Most motors can only tolerate a limited amount of starts in a period of time.

EVEN with a VFD you are limited. Also those fast stops ADD heat to the windings as well. 

IF fast starts are needed then you HAVE to go UP on /torque to get the job done faster. THEN you have an inertia problem with larger framed motors (;-) It gets to be a vicious circle with no end in sight.  LIGHT inertia high torque servos are the answer

3 sec runs will not give most ac motors time to get to speed much less cool off before the next cycle begins.

Just a thought, (;-) TP

 

Ahhh ... the HEAT !
Great explanation!

Thanks Terry.

OK Terry,
 1 more.
What would the weak points be if using a stepper ?
Thanks,
Russ

Limited RPM/torqueband, smoothness  running  in velocity mode. YES you can micro step BUT there is always the torque tradeoff.

(;-) TP

OK so what did you decide to do?

(;-)TP

I have an AB drive and motor ready if needed but inquired with Automation Direct regarding their GS2 VFD and Marathon MicroMax motor combination to which the tech replied would most likely work fine as it is the larger motors that would be problematic regarding the heat.

I have other uses for the VFD and motor if it doesn't work out so will try it (if the project bid is successful).

Just hate to use a good servo axis set-up unnecessarily.

(;-)  THose are FAMOUS last words.

The tech replied would "most likely" work fine .

By the time you buy the VFD, Load resistor bank, VFD rated motor you are getting closer to a servodrive/motor in cost.

WE KNOW the servo drive/motor works(;-).

Just a thought, (;-) TP