[h3ndrix]

Hello,

I asked this on another forum as well but, didnt get enough answers.

I have a question that I cant seem to get my head around, would appreciate some help.

I have a 1.2 angle 3 phase stepper with 1000 line encoder. This means my motor does 300 steps for each full turn. However, if I understand correctly, the encoders line count of 1000, even though it becomes 4000 count, it can not be divided by 300, so...how does this work?

Btw, my drivers micro-stepping capabilities are 800, 1600, 3200, 6400, 12800, 25600, 51200,1000, 2000, 4000, 5000, 8000, 10000, 20000, 40000

Thanks.

[H500]

If you have a servo stepper drive, there is no need for the counts to be divisible into the steps. The stepper can be driven more or less like a brushless servo motor.

[Al_The_Man]

It is called the least input increment, and a stepper can only position to what ever the step resolution is, either in full or fractional stepping, a servo motor on the other hand has a least input increment as fine as the encoder resolution allows.
Al.

[h3ndrix]

So, does that mean that if my stepper can only position to the step resolution, either in full or fractional, the encoder wheel is always going to read in between two encoder lines and be inaccurate? I am speaking considering the above mentioned micro stepping capabilities of my driver.

[Al_The_Man]

The encoder should give a reading of where it is actually positioned at by the motor, unless you have some kind of special stepper drive system, the stepper is almost always an open loop servo, IOW not capable of PID control as is a closed loop servo motor.
Al..

[h3ndrix]

Hi,

There is a video of the drive I am using with the motor. Thats not me but a very similar seetup is being used in the video:

https://www.youtube.com/watch?v=ZMZdCcLQc4M

In this video, the motor has high position keeping ability and it also catches steps if stalled for short periods.

[Al_The_Man]

I see by your OP and the vid it uses a 3phase stepper motor which essentially is a 3phase PM servo motor.
Al.

[h3ndrix]

So what does that mean for stepping? How does that effect the steppers ability to step, or microstep? How can the stepper be accurate if the step of the angle never aligns with the lines of the encoder? Thanks.

[H500]

Leadshine hasn't explained in detail how their system works, but I'm guessing it acts more like a brushless servo motor than a stepper. The controller will use the feedback from the encoder to adjust the drive current. It doesn't need to step. Read up on field oriented control, if you want the technical details.

[h3ndrix]

Is there a way to find this out for sure? A way to tell, if its stepping or if its field oriented control? Thanks.

[Al_The_Man]

Often these are variable reluctance motors, they can be detected by making sure the motor wires are all open and then turn by hand to see if there is no, or very little detent, if so they are V.R.
Al.

[H500]

If you are concerned about it's accuracy, tape a laser pointer on the shaft and measure the distance between steps.