Hi,
depending on your budget you might consider AC servos. There are some very cheap Chinese made AC servos but of questionable quality, support and documentation.
Delta (Taiwanese manufactured in China) and DMM (Canadian manufactured in China) are two good quality brands that won't break the bank.
Any decent AC servo of sufficient power will blow ANY stepper into the weeds. They have very generous overload ratings, typically three to four times their rated torque.
As an example I have a 400W B2 series Delta servo. It has a native 160,000 count per rev encoder, 1.27Nm rated, 3.8Nm 10 sec overload at 3000rpm rated or 5000rpm max.
The driver takes 230VAC single phase input, ie no power supply required. The programmable drive has an overwhelming multitude of control modes which makes them superbly
flexible for just about any machine for any purpose. The servo/drive/cables/shipping to the US will cost about $380 from various EBay suppliers.
Most steppers will not make 1000 rpm, the loss of torque will mean they lose steps or stall before they reach 1000 rpm. A servo has a flat torque characteristic to rated
speed, often 3000 rpm or higher.
You might be able to represent to your professor that equipping with servos IS THE industrial solution and that your project would best prepare you for real world solutions
that servos are vastly preferred over steppers.
A slightly cheaper alternative to AC servos are closed loop steppers. You will no doubt see plenty of offerings. They are intermediately priced between servos and
open loop steppers.
The manufacturers will claim that they are faster, more powerful, never lose steps.......all pure BS. As I said above all steppers lose torque as speed increases,
a closed loop stepper is no different. A stepper will only ever lose a step if its overloaded by either excess load or the speed at which its being asked to operate at.
A closed loop driver will insert an extra step to try to 'catch up', but guess what.....the extra step suffers the same fate, it gets lost because the stepper is overloaded.
Closed loop steppers do have two advantages, namely interpolation between steps for increased resolution, and following error alarms. These advantages are bought at
a significant price increase over open loop steppers. Any well specified open loop stepper used within its limitations will never lose a step an so my recomendation
is either:
1) Open loop steppers of lowest possible inductance with highest possible voltage drivers and power supply....or
2) AC servos
Don't mess with Mr. InBetween, closed loop steppers.
Craig
Hi Craig
How do you go about deciding what size servo you require, my current stepper motor spec is attached. These are on a 3ft x 3ft bed machine. If I were to move to a 8ftx4ft size machine specifically for cutting timber, plastics and soft metals how do you determine your servo sizes?
Mark
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