Shopbot stepper motors do we need closed loop?

[giggler]

Hi,

I'm considering building a larger router say 8by4 foot and have read that shopbot have been using closed loop stepper motor control.

Have have some pacific science nema 34's and micro stepper drives 6410-006 but the datasheet shows they are not closed loop, like most stepper drives.

I do have a few logic level industrial encoders and want to know is it worth connecting these up to a Gecko G-Rex 100 controller which supports encoder input for step feedback? Is close loop required for the average shopbot sized router, with or without a proper spindle?

When would I see such a benifit using them in closed loop control? I am thinking of rack and pinion drives for x and y while the z will probably be a ball screw. Not sure if that helps?

I understand that in closed loop systems the drives and/or controller monitors the movement for differences and tries to compensate. How often does a shopbot style router require this compensation? (sorry if this is a silly question).

Thanks,

DC
www.tea-with.me.uk

[ger21]

Originally Posted by giggler I do have a few logic level industrial encoders and want to know is it worth connecting these up to a Gecko G-Rex 100 controller which supports encoder input for step feedback?

Unless you write you're own control software to do it, the G100 can't do closed loop.

Shopbot sells both closed loop (alpha) and standard models. The closed loop can cut twice as fast. You can buy the closed loop system that the Shopbot uses from Oriental Motor. They are NOT cheap.

But do you need closed loop steppers? A properly designed stepper system should not lose steps. Many machines still sold today use open loop steppers, including the Shopbot Standard, which uses Gecko drives.


For a lot less money, you can build a servo system that will be able to run faster and with higher resolution than a stepper system.

What you choose really depends on what you expect from the machine, and what the machine needs to do what you want it to. Gecko has a FAQ here that gives some direction in regards to choosing steppers or servos for your particular application.

http://www.cnczone.com/forums/showthread.php?t=52090