[bernardbryce]

Hi all,
I have a few very detailed questions on stepper motor drivers for whoever can answer them.

1 If Im driving steppers with Geckos... I move to a y position, and then machine a long line, by moving the x axis only.... At some point in time the y axis Gecko driver will go into power save mode. Will this cause a slight movement in the y axis? ie s slight step in the line.

2 There is a trim pot to adjust for smoothness.... is this compensating for motor non-linearity?

3 When designing a driver to generate step and direction signals, how smooth does the transitions between step frequencies need to be... For example if my timer has a resolution of 1uS I will be able to change from a pulse period of 1000uS to 999uS (around 1Khz) which is just 0.1% increase in frequency... this sounds smooth to me. but If im going from 10uS to 9uS we have a 10% jump which equates to a full 10Khz jump... is there a sensible rule of thumb, and dose it depend on the level of microstepping (eg x10 in this case)

Any help appreciated
Bernard

[ger21]

1) only if the cutting forces are higher than the motor can hold.

2) don't know.

3) don't know.

[bernardbryce]

Cheers. I guess that both motor phase currents are pulled back proportionally to maintain position even while microstepping... There are practically no cutting forces in this application.
Bernard

[RCaffin]

'Power save' does not mean 'power loss'. A stepper needs a lot less power to hold a position than to move. So going into power save mode does not mean the stepper will suddnely start to move.

Technically, yes, there may be a slight movement. Maybe 1/2 to 1/4 of the basic micro-step distance. I suspect that will be in the 'few microns' zone, or less.

Cheers

[morestuff]

2 There is a trim pot to adjust for smoothness.... is this compensating for motor non-linearity?

Yes, it adjusts for motor magnetic linearity. Many people confuse this with
mid-band anti-resonance suppression. The mid-band anti-resonance is always
active and is not adjustable on the G540. Some of the G200 series drivers
have a jumper to select large (NEMA 42) versus regular (NEMA 34 and smaller)
motors to better match the anti-resonance to the motor.

Regards,
Steve Stallings
PMDX.COM - Products for CNC and motion control applications