the first few microsteps

[stirling]

I'm posting this here because I use Gecko drives but I suppose my question is about microstepping drives generally. Hope that's ok. Also I've searched and can't see if this has been discussed before.

When a system is turned off the motors are more than likely somewhere between full steps and if the system is mechanically "tight" then presumably that's where they'll stay. So, now the system is turned back on again. The drives as far as I'm aware don't have memory so presumably as they get step signals they energise the coils through their 10 microstep sequence BUT starting as if the motors WERE on a full step position to start with. So... presumably (sorry - lots of presumablys here) until the microstepping gets back in synch with the ACTUAL position of the motor, the motors either don't move or perhaps even "jitter" a bit. Am I on the right lines here?

Reason I'm asking is because some motion controlers I've seen "save" the last coord position before shutdown and start up again there, and some don't. Seems to me those that save the position shouldn't - due to my thinking above. Right?/Wrong? - just wondering.

Thanks

Ian

[Mariss Freimanis]

The assumption is anytime you use a step motor drive (or a servodrive) is you will home it to a known location immediately after power-up. It is dangerous to assume an incremental device like a step motor will "remember" its position between power-up cycles. The drive cannot be expected to note any change in the motor position while it is dead (not powered).

Can you more fully describe your application that may help to give you what you need?

Mariss

[stirling]

Thanks Mariss
No actual problem - just wanted confirmation or otherwise that my understanding is correct. Just delving into some of the minutiae for the fun of learning.

Clearly as you say "The drive cannot be expected to note any change in the motor position while it is dead (not powered)." but I was also saying (and checking if I was correct) that it can't be expected to know which microstep it was on even if the motor DOESN'T change position"

Ian

[pminmo]

Originally Posted by stirling I'm posting this here because I use Gecko drives but I suppose my question is about microstepping drives generally. Hope that's ok. Also I've searched and can't see if this has been discussed before. When a system is turned off the motors are more than likely somewhere between full steps and if the system is mechanically "tight" then presumably that's where they'll stay. So, now the system is turned back on again. The drives as far as I'm aware don't have memory so presumably as they get step signals they energise the coils through their 10 microstep sequence BUT starting as if the motors WERE on a full step position to start with. So... presumably (sorry - lots of presumablys here) until the microstepping gets back in synch with the ACTUAL position of the motor, the motors either don't move or perhaps even "jitter" a bit. Am I on the right lines here? Reason I'm asking is because some motion controlers I've seen "save" the last coord position before shutdown and start up again there, and some don't. Seems to me those that save the position shouldn't - due to my thinking above. Right?/Wrong? - just wondering. Thanks Ian

Unless it's a closed loop system with absolute encoders, the system HAS to determine it's physical location by some method which means movement to establish an absolute machine location.