VSD-e & Linear motor resolution

[pixpop]

If I'm using a VSD-e with a linear motor, and I want 0.001 inch resoution, should I get a linear encoder with 250 cycles per inch? Or do I need 1000 cycles per inch?

[Jason3]

Hi there,

I'd suggest you get an encoder with a finer resolution as this will give better motor control and higher accuracy, then use the pulse multiplier in GDTool to make each input pulse = 0.001" and turn on the input pulse smoothing.

Best regards,

Jason

[pixpop]

Jason, thanks for the input. However it doesn't answer my question: If I have a linear encoder with 250 cycles per inch, what resolution will I get? Will it be 1/250 inch, or 1/1000 inch?

[Jason3]

So sorry - if you get an encoder with 250 lines per inch, it will be 0.001" resolution after 4x decoding, so one input pulse from your control will result in a move of 0.001" assuming the multiplier in GDTool is set to 1:1. However, I have been wrong about the quadrature decoding before, so if I am wrong again, hopefully Tero will correct me and give you a definitive answer!

Best regards,

Jason

[H.O]

Hi,
250 cycles/inch will give you a resolution of 0.001. However, you generally want an encoder resolution many times higher than the positioning resolution that you're aiming for.

In the above case with 0.001 resolution the motor can be 0.000999 from target position without the drive knowing about it. If you're aiming for 0.001 resolution "at the mechanics" then go for 1000 cycles/inch scales - at least.

[Xerxes]

Yes, 250 lines gives 1000 counts per unit. If you need 1/1000" precision, then its good to have at least 1/10000" resolution encoder.