Motion precision and microstepping

[plessnick]

Hello,

I've a customer that need to achieve a 0.01 degree accuracy on some rotation movement.   All the motion hardware come from NI.  The drive is a NI-7602 with 256 microsteps.  The gearing ratios give 0.288 degree per step for one axe and 0.36 degree for a second axe.  There are no encoders on the system for mechanical reasons.  The system is subject to +/-3g vibrations from a few Hz to 3kHz.

Using 256 microsteps, the customer should achieve accuracy near 0.001-0.0015.  However, I've read that microstepping is subject to non-linear error.  Would this error avoid us to reach the needed accuracy of 0.01 degree?  Does anyone has an idea on how microstepping would be affected by system vibrations?

Regards,

Patrick

[Vivek_N]

Hello,

As you mentioned, large non-linearities may be observed with microstepping. Unfortunately, it is not posiible to set a benchmark on how large the errors may be as this is dependent on the mechanical system itself as well. The following knowledgebase article mentions a method to improve accuracy of your motor movements: http://digital.ni.com/public.nsf/allkb/27FFF2E1E017848C86256F11006AA23E?OpenDocument. 

I hope this helps. 

[Jochen]

Patrick,

in order to specify the accuracy of your system you will have to find a way to measure it (encoder, laser interferometer,...). From my own experience microstepping beyond a factor of 100 doesn't add significant accuracy because of the mentioned non-linearities. In general extended accuracy should be created by using high quality gear boxes instead of excessivemicrostepping factors.

Jochen

[plessnick]

Hello,

I'd like to thank you both for your answer.  I agreed that good quality gearing would have solved the problem but the system was already designed when I came in the project.

Patrick