Thanks for the detailed information Craig, also to u Steve, so we can say that microstepping is ideal for cnc machines like laser/plasma/water jet cutters or small machinery like pick and place machines which has light weighted gantries.

In my case the ideal is full step as it seems because i need the full torque from the 16nm motor, x axis motor is driving the heaviest weight in this machine.

Hakan

Hi,
I would still use microstepping, say 1/5, 1/8, 1/10, or 1/16, to get advantage of the smoothness of motion, but when you consider your machines
'actual' resolution, calculate it as if you are using 1/2 steps, while the 'theoretical' resolution would be 1/5 or 1/8 or whatever provided there was zero load
on the stepper.

In short what you have done by implementing 1/10 th stepping is good, you get the smoothness that you want but the actual resolution will be 10um,
not 2um as you previously calculated. Still 10um is pretty damn good for any machine!

Craig

For most machine tools the best way to get higher resolution is to used a closed loop system with feedback that can measure the desired resolution and a driver that takes advantage of it.

If you want to gain more resolution from an open loop stepper using microstepping, then utilize motors with much higher torque so that the error in the angular location is not affected as much by the available torque at the microstepped locations.

For smoothness of open loop stepper systems, I usually recommend microstepping factors between 4 and 10 which do smooth things significantly without adding too much challenge to the process of generating and transmitting the step signals.

I have an 11nm servo motor for the X axis but its gservo(made in china) brand and it does not have an auto tuning software so u have to tune it by your self manually, need to be connected to the load to adjust the gain parameters, actually i did that at first but while playing with some parameters motor did a very strange resonance it was so high that the plastic between 2 piece servo coupling literally melted. It was connected to the ballscrew at that time, it is a c3 zero backlash ballscrew which is little bit expensive so i was afraid that the balls in the nut damaged the ballscrew but again God helped and it didnt do any harm. After that incident i afraid to harm the ballscrew and removed the servo and put the stepper, thats why i am going on with the open loop stepper.

when i get a yaskawa, panasonic or delta in equivelant torque(16-20Nm) i will change it with servo, those brands have auto tuning softwares with oscilloscope screens etc. as u know.

For guys like you, who knows the details about the stuff it may be easy to tune a servo manually but guys like me who is relatively new in this stuff its a little bit risky.

Hakan

Hi,
closed loop steppers do offer an advantage of higher resolution, but that's about the only advantage. The manufacturers claim 'they
go faster, more power, never lose steps'....pure BS. Closed loop steppers are still steppers and they lose torque at speed just like any stepper,
closed loop doesn't do squat about that.

If you want true closed loop performance, don't waste your money on closed loop steppers, get servos. A servo will eat any stepper ever made.

Craig

Hi,
what sort of machine requires 16Nm?

I have bought and used 750W Delta B2 series servos which are 2.4Nm rated, and 7.1Nm overload and they kick arse!
While I can get 25m/min rapids and 0.25g accels, its too aggressive and I back in off to 15m/min and 0.15g....and that's still scary fast.

Craig

Hi Craig,

This is a prototype machine that we built, its a 4 ton machine in total with 1200mm x 800mm x 500mm machining area and the x axis is the heaviest axis because u know there is y and zth axis connected to the ballscrew(its a 2 column machine like dmg dmu 340) so u have to push them at reasonable speeds and with 10um precision, now i can drive the x axis with 6000mm/minute but even with 40mm diameter 5mm pitch ballscrew and precisely leveled roller guideways 16nm is not enough(to precisely cut a perfect circle for example)in higher accelerations/speeds so i am looking for a 20Nm yaskawa or panasonic servo for the x axis.

On the other hand i saw that 11nm servo motor moved the 4 ton body front and back couple centimeters when it made sudden movements on x axis because of the inertia but for precision positioning i think its better if the torque is higher then needed.

Delta is also nice but its my second choice because approx. same price you can buy a yaskawa/panasonic from China or even from ebay if u catch the right bid.

Hakan

Hi,

Delta is also nice but its my second choice because approx. same price you can buy a yaskawa/panasonic from China or even from ebay if u catch the right bid.

All the sites I seen selling Yaskawa are  double and triple for the equivalent Delta.

Craig

Hi,
I did the calculations with my 32mm diameter 5mm pitch screws and the inertia is totally dominated by the rotational inertia of the ballscrew, not the 150kg axis weight.

The breakdown went like this:
85% rotational inertia of the ballscrew
10% rotational inertia of the servo rotor
5% linear inertia of the axis.

Given that the first moment of inertia of a ballscrew goes as the fourth power of diameter I would guess you situation more like 92% of the inertia is in the ballscrew.
Why such large diameter screws? Mine were outsized at 32mm...but they were what I could get.

Craig

Hi Craig,

u can check taobao.com u can get good equipment from there with good prices sometimes.

I got the diameter big for stiffness, i am driving the axis from one side, u should drive that kind of axis from double side normally, if u do so u can use smaller diameter(32mm) ballscrews but if u do it on one side for the machining precision bigger diameter is the better.

Hakan