Stepper motor step resolution up to 50000?

[thitchen007]

The full step resolution is 200. I learned that by software configuration, the step resolution can be hugely increased to 50000.

(Page 9 in "Getting Started with NI 7330/7340/7350 Motion Controllers and P7000 Series Stepper Drives")

Getting Started with NI 7330/7340/7350 Motion Controllers and P7000 Series Stepper Drives

I'm wondering how do they do this?

I learned that people can do "microstepping" to increase step resolution, but the accuracy of each microstep tends to be compromised. (http://homepage.cs.uiowa.edu/~jones/step/micro.html)

If this is the case then I would like to avoid such a "software configed microstep".

Or please if anyone can tell me how do NI achieves this.

Thanks in advanced.

[National_Burritos]

Hi thitchen007,

Out of curiosity, what motor are you using? If the motor has 200 steps per revolution, then increasing that to 50,000 would be acheived by microstepping. If you are using a p7000 Stepper drive, then these settings would be configured by the DIP switches on the p7000 drive, as denoted in the manual you referred.

For more information on this, I would recommend this NI white paper: http://www.ni.com/white-paper/10638/en/

I hope this helps!

[thitchen007]

Hi Rahul,

Thanks for your reply.

My motor is the legacy one with 200 steps per revolution.

I am using the p7000 stepper drive, I read the white paper, my question is: isn't it the same concept of microstepping when you configure over the DIP switches? Anyway the teeth number is fixed to 50, I couldn't see any other way to increase the resolution to 50000.

If either way is using microstepping, then the accuracy of each step will be decreased by any means.

[National_Burritos]

Hello,

Microstepping is basically the partial energizing of certain electromagnets in the motor to allow for partial movement of the rotor/smaller increments. As you mentioned, this results in smoother motion at slower speeds and improved resolution.

As the white paper touched upon, there is a loss in holding torque because the stator and rotor of the motor do not align perfectly at each step. Also, the non-linearities introduced in position are due to the fact that smaller steps will not necessarily be of equal distance in separation. However, these shouldn't greatly affect your system; though that depends on your end goals.

EIther way, microstepping is controlled by the stepper drive and is a property of whether your drive supports that function or not; it is not necessarily a property of the motor. The DIP switches allow you to configure the drive to control the motor to operate with a certain number of steps per revolution.

[Buechsenschuetz]

As mentioned by others, increasing the number of steps per revolution or, as this procedure is usually called. using microstepping is rather a feature of the driver unit you want to use. Driver units in most cases have a feature to select the number of microsteps per full step of the motor. So if you are using a motor with 200 steps per revolution you have to use a microstepping rate of 250 to achieve 50000 microsteps per revolution. The procedure of selecting the microstep rate is different, some use configuration switches or jumpers, some use a configuration software (which, of course, requires some kind of data transfer between a PC and the driver unit).

However, it is not adviseable to use the highest microstepping rate possible. First of all, this will NOT necessarily increase positioning accuracy. For precise positioning you need a feedback device (either a rotary or a linear encoder), and the resolution of the feedback device must at least equal the step resolution of the motor or should be higher if possible. I do not know any rotary encoders with more than a few thousand steps per revolution.

Second, it is a very popular misunderstanding that the higher the microstepping rate the higher the postioning accuracy will be. As mentioned, the accuracy of the system depends mainly on the resolution and accuracy of the feedback device. Also, microsteps will not be equally wide, there will be a deviation from linear interpolation between full steps. There are motors designed for optimum torque and there are motors deisgned for optimum microstepping accuracy - usually you can not have both at the same time.

From my and my colleagues' experience, microstepping rates between 10 and 50 are reasonable values. So a motor with 200 full steps per revolution will run at 2000...10000 steps per revolution.

Of course you have to set the correct "steps per revolution" values in your software.